description: British mathematician John Littlewood once said about Indian mathematician Srinivasa Ramanujan that "every positive integer was one of his personal friends."
  
  It turns out that positive integers can also be friends with each other! You are given an array a of distinct positive integers. 
  
  Define a subarray a_i, a_{i+1}, …, a_j to be a friend group if and only if there exists an integer m ≥ 2 such that a_i mod m = a_{i+1} mod m = … = a_j mod m, where x mod y denotes the remainder when x is divided by y.
  
  Your friend Gregor wants to know the size of the largest friend group in a.
  
  Input
  
  Each test contains multiple test cases. The first line contains the number of test cases t (1 ≤ t ≤ 2⋅ 10^4). 
  
  Each test case begins with a line containing the integer n (1 ≤ n ≤ 2 ⋅ 10^5), the size of the array a.
  
  The next line contains n positive integers a_1, a_2, …, a_n (1 ≤ a_i ≤ {10}^{18}), representing the contents of the array a. It is guaranteed that all the numbers in a are distinct.
  
  It is guaranteed that the sum of n over all test cases is less than 2⋅ 10^5.
  
  Output
  
  Your output should consist of t lines. Each line should consist of a single integer, the size of the largest friend group in a.
  
  Example
  
  Input
  
  
  4
  5
  1 5 2 4 6
  4
  8 2 5 10
  2
  1000 2000
  8
  465 55 3 54 234 12 45 78
  
  
  Output
  
  
  3
  3
  2
  6
  
  Note
  
  In the first test case, the array is [1,5,2,4,6]. The largest friend group is [2,4,6], since all those numbers are congruent to 0 modulo 2, so m=2.
  
  In the second test case, the array is [8,2,5,10]. The largest friend group is [8,2,5], since all those numbers are congruent to 2 modulo 3, so m=3.
  
  In the third case, the largest friend group is [1000,2000]. There are clearly many possible values of m that work.
solution: //------------------>>>>>>>>>>>>>>>> HI . HOW ARE YOU? <<<<<<<<<<<<<<<<<<<<<<<<<<<<<------------------------------
  
  import java.io.*;
  import java.util.*;
  import java.util.List;
  import java.util.StringTokenizer;
  
  //---------------------------->>>>>>>>>>>>>>>>>>>>>> FK OFF <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<-------------------
  
  //--------------------------->>>>>>>>>>>>>>>>>>>>>>>> HACKER MF <<<<<<<<<<<<-------------------------------------
  
  public class practice{
  
      static int[] count,count1,count2;
      static boolean[] prime;
      static boolean flag;
      static int[] spf;
      static Node[] nodes,nodes1,nodes2;
      static long[] arr;
      static long[][] cost;
      static int[] arrInt,darrInt,farrInt;
      static int[][] dp;
      static char[] ch,ch1,ch2;
      static long[] darr,farr;
      static long[][] mat,mat1;
      static boolean[] vis;
      static long x,h;
      static long maxl,sum,total;
      static double dec;
      static long mx = (long)1e7;
      static long inf = (long)1e17;
      static String s,s1,s2,s3,s4;
      static long minl;
      static long mod = (long)(1e9)+7;
      // static int minl = -1;
      // static long n;
      static int n,n1,n2,q,r1,c1,r2,c2;
      static int arr_size = (int)2e5+10;
      static long a;
      static long b;
      static long c;
      static long d;
      static long y,z;
      static int m,m1;
      static long ans;
      static long k;
      static FastScanner sc;
      static String[] str,str1;
      static Set<Long> set,set1,set2;
      static SortedSet<Long> ss;
      static List<StringBuilder> list,list1,list2,list3;
      static PriorityQueue<Node> pq,pq1;
      static LinkedList<Node> ll,ll1,ll2;
      static Map<Integer,List<Integer>> map;
      static Map<Integer,Integer> map2;
      static Map<Integer,Long> mapL,mapR;
      static Map<Integer,Node> map1;
      static StringBuilder sb,sb1,sb2;
      static int index;
      static int[] dx = {0,-1,0,1,-1,1,-1,1};
      static int[] dy = {-1,0,1,0,-1,-1,1,1};
  
      static class Node{
          long first;
          int second;
          Node(long f,int s){
              this.first = f;
              this.second = s;
          }
      }
  
      static LNode head = null;
      static LNode tail = null;
  
      static class LNode{
          long key;
          long val;
          LNode next;
          LNode prev;
          LNode(long key,long val){
              this.key = key;
              this.val = val;
              this.next = null;
              this.prev = null;
          }
          LNode(long val){
              this.key = -1;
              this.val = val;
              this.next = null;
              this.prev = null;
          }
      }
  
  
  //     public static void solve(){
  //
  //        FastScanner sc = new FastScanner();
  //        int t = sc.nextInt();
  //        // int t = 1;
  //        for(int tt = 1 ; tt <= t ; tt++){
  //
  //            System.out.println("Case #"+tt+": "+ ans);
  //
  //        }
  //
  //     }
  
      //--------------->>>>IF YOU ARE HERE FOR QUICKSORT HACK THEN SORRY NO HACK FOR YOU<<<-------------------------------
  
      public static void solve(){
  
          //dont forget to change array to its difference and take abs
          n -= 1;
          arr = new long[n];
          for(int i = 1 ; i <= n ; i++){
              arr[i-1] = abs(darr[i] - darr[i-1]);
          }
  
          int l = 0;
          int h = n+1;
          long[] suffix;
          long[] prefix;
  
          while(h - l > 1){
  
              int mid = (h + l)/2;
  
              suffix = new long[n];
              prefix = new long[n];
              boolean flag = false;
  
              for(int j = 0; j < n; j++)
                  if (j%mid == 0)
                      prefix[j] = arr[j];
                  else
                      prefix[j] = gcd(prefix[j - 1], arr[j]);
  
              for(int j = n - 2; j >= 0; j--)
                  if (j%mid == mid-1)
                      suffix[j] = arr[j];
                  else
                      suffix[j] = gcd(suffix[j + 1], arr[j]);
  
  
              for(int j = 0; j < n - mid + 1 ; j++) {
                  if (gcd(suffix[j], prefix[j + mid - 1]) >= 2L) {
                      flag = true;
                      break;
                  }
                  if (((j % mid) == (mid - 1)) && prefix[j] >= 2L) {
                      flag = true;
                      break;
                  }
              }
  
              if (flag)
                  l = mid;
              else
                  h = mid;
  
          }
  
          sb.append(l+1).append("\n");
  
      }
  
      //----------->>>>>>> SPEED UP SPEED UP . THIS IS SPEEDFORCES . SPEED UP SPEEEEEEEEEEEEEEEEEEEEEEEEEEDDDDDD <<<<<<<------------------
  
      public static void main(String[] args) {
  
          sc = new FastScanner();
          // Scanner sc = new Scanner(System.in);
          sb = new StringBuilder();
          int t = sc.nextInt();
  //        int t = 1;
          while(t > 0){
  
  //             k = sc.nextLong();
              // x = sc.nextLong();
              // y = sc.nextLong();
              // z = sc.nextLong();
  
  //            a = sc.nextLong();
  //             b = sc.nextLong();
  //             c = sc.nextLong();
  //             d = sc.nextLong();
  //
  //             x = sc.nextLong();
  //             y = sc.nextLong();
  //             z = sc.nextLong();
              // d = sc.nextLong();
  
              n = sc.nextInt();
  
              // n1 = sc.nextInt();
  
  //            m = sc.nextInt();
  //             q = sc.nextInt();
  
  //             a = sc.nextLong();
  //             b = sc.nextLong();
  
  //             k = sc.nextLong();
  
  //            x = sc.nextLong();
              // d = sc.nextLong();
  
  //            s = sc.next();
  
  //            ch = sc.next().toCharArray();
  //            ch1 = sc.next().toCharArray();
  
  //             m = sc.nextInt();
              // n = 6;
  
  //            arr = new long[n];
  //            for(int i = 0 ; i < n ; i++){
  //                arr[i] = sc.nextLong();
  //            }
  
  //            arrInt = new int[n];
  //            for(int i = 0 ; i < n ; i++){
  //                arrInt[i] = sc.nextInt();
  //            }
  
              // x = sc.nextLong();
              // y = sc.nextLong();
  //             ch = sc.next().toCharArray();
  //            m = n;
  ////             m = sc.nextInt();
              darr = new long[n];
              for(int i = 0 ; i < n ; i++){
                  darr[i] = sc.nextLong();
              }
              // k = sc.nextLong();
              // m = n;
  //             darrInt = new int[n];
  //             for(int i = 0 ; i < n ; i++){
  //                 darrInt[i] = sc.nextInt();
  //             }
  
  //             farr = new long[n];
  //             for(int i = 0 ; i < n ; i++){
  //                 farr[i] = sc.nextLong();
  //             }
  
              // farrInt = new int[m];
              // for(int i = 0; i < m ; i++){
              //     farrInt[i] = sc.nextInt();
              // }
  
              // m = n;
  //            mat = new long[n][m];
  //            for(int i = 0 ; i < n ; i++){
  //                for(int j = 0 ; j < m ; j++){
  //                    mat[i][j] = sc.nextLong();
  //                }
  //            }
  
  //             m = n;
  //             mat = new char[n][m];
  //             for(int i = 0 ; i < n ; i++){
  //                 String s = sc.next();
  //                 for(int j = 0 ; j < m ; j++){
  //                     mat[i][j] = s.charAt(j);
  //                 }
  //             }
  //
  //             str = new String[n];
  //             for(int i = 0 ; i < n ; i++)
  //                 str[i] = sc.next();
  
  //             nodes = new Node[n];
  //             for(int i = 0 ; i < n ;i++)
  //                 nodes[i] = new Node(sc.nextLong(),(i));
  
              solve();
              t -= 1;
          }
          System.out.print(sb);
  
      }
  
      public static int log(double n,double base){
  
          if(n == 0 || n == 1)
              return 0;
  
          if(n == base)
              return 1;
  
          double num = Math.log(n);
          double den = Math.log(base);
  
          if(den == 0)
              return 0;
  
          return (int)(num/den);
      }
  
      public static boolean isPrime(long n) {
          // Corner cases
          if (n <= 1)
              return false;
  
          if (n <= 3)
              return true;
  
          // This is checked so that we can skip
          // middle five numbers in below loop
          if (n%2 == 0 || n%3 == 0)
              return false;
  
          for (int i=5; i*i<=n; i=i+6)
              if (n%i == 0 || n%(i+2) == 0)
                  return false;
  
          return true;
      }
  
      public static void SpecialSieve(int MAXN)
      {
          spf = new int[MAXN];
          spf[1] = 1;
          for (int i=2; i<MAXN; i++)
  
              // marking smallest prime factor for every
              // number to be itself.
              spf[i] = i;
  
          // separately marking spf for every even
          // number as 2
          for (int i=4; i<MAXN; i+=2)
              spf[i] = 2;
  
          for (int i=3; i*i<MAXN; i++)
          {
              // checking if i is prime
              if (spf[i] == i)
              {
                  // marking SPF for all numbers divisible by i
                  for (int j=i*i; j<MAXN; j+=i)
  
                      // marking spf[j] if it is not
                      // previously marked
                      if (spf[j]==j)
                          spf[j] = i;
              }
          }
      }
  
      public static ArrayList<Integer> getFactorization(int x)
      {
          ArrayList<Integer> ret = new ArrayList<Integer>();
          while (x != 1)
          {
              ret.add(spf[x]);
              x = x / spf[x];
          }
          return ret;
      }
  
      public static long gcd(long a, long b)
      {
          if (b == 0)
              return a;
          return gcd(b, a % b);
      }
  
      public static long lcm(long a, long b)
      {
          return (b/gcd(b, a % b)) * a;
      }
  
      public static long mod_inverse(long a,long mod){
          long x1=1,x2=0;
          long p=mod,q,t;
          while(a%p!=0){
              q = a/p;
              t = x1-q*x2;
              x1=x2; x2=t;
              t=a%p;
              a=p; p=t;
          }
          return x2<0 ? x2+mod : x2;
      }
  
      public static void swap(double[] curr,int i,int j){
          double temp = curr[j];
          curr[j] = curr[i];
          curr[i] = temp;
      }
  
      static final Random random=new Random();
  
      static void ruffleSortLong(long[] a) {
          int n=a.length;//shuffle, then sort
          for (int i=0; i<n; i++) {
              int oi=random.nextInt(n);
              long temp=a[oi];
              a[oi]=a[i]; a[i]=temp;
          }
          Arrays.sort(a);
      }
  
      static void ruffleSortInt(int[] a) {
          int n=a.length;//shuffle, then sort
          for (int i=0; i<n; i++) {
              int oi=random.nextInt(n);
              int temp=a[oi];
              a[oi]=a[i]; a[i]=temp;
          }
          Arrays.sort(a);
      }
  
      static void ruffleSortChar(char[] a) {
          int n=a.length;//shuffle, then sort
          for (int i=0; i<n; i++) {
              int oi=random.nextInt(n);
              char temp=a[oi];
              a[oi]=a[i]; a[i]=temp;
          }
          Arrays.sort(a);
      }
  
      static long binomialCoeff(long n, long k){
  
          long res = 1;
  
          // Since C(n, k) = C(n, n-k)
          if (k > n - k)
              k = n - k;
  
          // Calculate value of
          // [n * (n-1) *---* (n-k+1)] / [k * (k-1) *----* 1]
          for (long i = 0; i < k; ++i) {
              res = (res*(n - i));
              res = (res/(i + 1));
          }
  
          return res;
      }
  
      static long mod(long x)
      {
          long y = mod;
          long result = x % y;
          while (result < 0)
          {
              result += y;
          }
          return result;
      }
  
      static long[] fact;
  
      public static long inv(long n){
          return power(n, mod-2);
      }
  
      public static void fact(int n){
          fact = new long[n+1];
          fact[0] = 1;
          for(int j = 1;j<=n;j++)
              fact[j] = (fact[j-1]*(long)j)%mod;
      }
  
      public static long binom(int n, int k){
  
          long prod = fact[n];
          prod*=inv(fact[n-k]);
          prod%=mod;
          prod*=inv(fact[k]);
          prod%=mod;
          return prod;
      }
  
      static long power(long x, long y){
          if (y == 0)
              return 1;
          if (y%2 == 1)
              return (x*power(x, y-1))%mod;
          return power((x*x)%mod, y/2)%mod;
      }
  
      static void sieve(int n){
  
          prime = new boolean[n+1];
          for(int i=2;i<n;i++)
              prime[i] = true;
  
          for(int p = 2; p*p <=n; p++)
          {
              if(prime[p])
              {
                  for(int i = p*p; i <= n; i += p)
                      prime[i] = false;
              }
          }
  
      }
  
      static long abs(long a){
          return Math.abs(a);
      }
  
      static int abs(int a){
          return Math.abs(a);
      }
  
      static int max(int a,int b){
          if(a>b)
              return a;
          else
              return b;
      }
      static double max(double a,double b){
          if(a>b)
              return a;
          else
              return b;
      }
      static double min(double a,double b){
          if(a>b)
              return b;
          else
              return a;
      }
  
      static int min(int a,int b){
          if(a>b)
              return b;
          else
              return a;
      }
  
      static long max(long a,long b){
          if(a>b)
              return a;
          else
              return b;
      }
  
      static long min(long a,long b){
          if(a>b)
              return b;
          else
              return a;
      }
  
      static long sq(long num){
          return num*num;
      }
  
      static double sq(double num){
          return num*num;
      }
  
      static long sqrt(long num){
          return (long)Math.sqrt(num);
      }
  
      static double sqrt(double num){
          return Math.sqrt(num);
      }
  
      static private void removeNode(LNode n){
          if(n.prev!=null){
              n.prev.next = n.next;
          }else{
              head = n.next;
          }
  
          if(n.next!=null){
              n.next.prev = n.prev;
          }else{
              tail = n.prev;
          }
      }
  
      static private void offerNode(LNode n){
  
          if(tail!=null){
              tail.next = n;
          }
  
          n.prev = tail;
          n.next = null;
          tail = n;
  
          if(head == null){
              head = tail;
          }
      }
  
      static class FastScanner {
  
          BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
          StringTokenizer st=new StringTokenizer("");
          String next() {
              while (!st.hasMoreTokens())
                  try {
                      st=new StringTokenizer(br.readLine());
                  } catch (IOException e) {
                      e.printStackTrace();
                  }
              return st.nextToken();
          }
  
          int nextInt() {
              return Integer.parseInt(next());
          }
          //        void readArray(int n) {
  //            arr = new long[n];
  //            for (int i = 0; i < n; i++)
  //                arr[i] = nextLong();
  //        }
          long nextLong() {
              return Long.parseLong(next());
          }
      }
  
  }