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: import java.util.*;
  import java.math.*;
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.util.StringTokenizer;
  
  
  public class b{ 
  
       static FastScanner sc;
       static TreeSet<Integer> ans;
       static long[] arr,a,dp;
       static char[][] board;
       static long mul,mul1;
       static int[] spf;
       static char[] ch;
       static int n,q,m;
       static long k,x;
       static StringBuilder sb;
       static long b,sum;
       static Map<Integer,List<Integer>> map;
      static Map<Long,List<Integer>> map2;
      static Map<Long,List<Integer>> map3;
      static Map<Integer,Integer> shortest;
      static Map<Integer,List<Integer>> map1;
      static List<Integer> list,list1;
      static int[] count;
  
      // static class Node{
      //     long dist;
      //     Set<Integer> set;
      //     Node(){
      //         this.set = new HashSet<>();
      //     }
      //     Node(int f){
      //         this.dist = f;
      //         this.set = new HashSet<>();
      //     }
      // }
  
      // public static class Lca {
  
      //     int[] depth;
      //     int[] dfs_order;
      //     int cnt;
      //     int[] first;
      //     int[] minPos;
      //     int n;
  
      //     void dfs(List<Integer>[] tree, int u, int d) {
      //         depth[u] = d;
      //         dfs_order[cnt++] = u;
      //         for (int v : tree[u])
      //             if (depth[v] == -1) {
      //                 dfs(tree, v, d + 1);
      //                 dfs_order[cnt++] = u;
      //             }
      //     }
  
      //     void buildTree(int node, int left, int right) {
      //         if (left == right) {
      //             minPos[node] = dfs_order[left];
      //             return;
      //         }
      //         int mid = (left + right) >> 1;
      //         buildTree(2 * node + 1, left, mid);
      //         buildTree(2 * node + 2, mid + 1, right);
      //         minPos[node] = depth[minPos[2 * node + 1]] < depth[minPos[2 * node + 2]] ? minPos[2 * node + 1] : minPos[2 * node + 2];
      //     }
  
      //     public Lca(List<Integer>[] tree, int root) {
      //         int nodes = tree.length;
      //         depth = new int[nodes];
      //         Arrays.fill(depth, -1);
  
      //         n = 2 * nodes - 1;
      //         dfs_order = new int[n];
      //         cnt = 0;
      //         dfs(tree, root, 0);
  
      //         minPos = new int[4 * n];
      //         buildTree(0, 0, n - 1);
  
      //         first = new int[nodes];
      //         Arrays.fill(first, -1);
      //         for (int i = 0; i < dfs_order.length; i++)
      //             if (first[dfs_order[i]] == -1)
      //                 first[dfs_order[i]] = i;
      //     }
  
      //     public int lca(int a, int b) {
      //         return minPos(Math.min(first[a], first[b]), Math.max(first[a], first[b]), 0, 0, n - 1);
      //     }
  
      //     int minPos(int a, int b, int node, int left, int right) {
      //         if (a == left && right == b)
      //             return minPos[node];
      //         int mid = (left + right) >> 1;
      //         if (a <= mid && b > mid) {
      //             int p1 = minPos(a, Math.min(b, mid), 2 * node + 1, left, mid);
      //             int p2 = minPos(Math.max(a, mid + 1), b, 2 * node + 2, mid + 1, right);
      //             return depth[p1] < depth[p2] ? p1 : p2;
      //         } else if (a <= mid) {
      //             return minPos(a, Math.min(b, mid), 2 * node + 1, left, mid);
      //         } else if (b > mid) {
      //             return minPos(Math.max(a, mid + 1), b, 2 * node + 2, mid + 1, right);
      //         } else {
      //             throw new RuntimeException();
      //         }
      //     }
      // }
  
      // private static long dfs(int v, int parent,long ht) {
  
      //     List<Integer> list = map.get(v);
      //     hyt[v] = ht;
  
      //     if(list.size() == 1){
      //         if(!map3.containsKey(ht))
      //             map3.put(ht,new ArrayList<>());
  
      //         map3.get(ht).add(v);
      //         return ht;
  
      //     }
  
      //     long maxl = -1;
      //     for(Integer i : list){
      //         if(i == parent)
      //             continue;
      //         maxl = Math.max(maxl,dfs(i,v,ht+1));
      //     }
  
      //     return maxl;
  
      // }
      // public static int N = 100005;
  
      // long a[N];
      // long sfx[N];
      // long pfx[N];
  
      public static boolean f(int width){
  
          // long[] a = new long[n];
          long[] sfx = new long[n];
          long[] pfx = new long[n];
  
          for (int j = 0; j < n; j++){
              if (j % width == 0){
                  pfx[j] = a[j];
              }
              else pfx[j] = gcd(pfx[j - 1], a[j]);
          }
          for (int j = n - 2; j >= 0; j--){
              if (j % width == width - 1){
                  sfx[j] = a[j];
              }
              else sfx[j] = gcd(sfx[j + 1], a[j]);
          }
  
          for(int j = 0; j < n - width + 1 ; j++){
              if (gcd(sfx[j], pfx[j + width - 1]) >= k) return true;
              if (((j % width) == width - 1) && pfx[j] >= k){
                  return true;
              }
          }
          return false;
      }
  
  
      public static int solve(){
  
          int lo = 0;
          int hi = n+1;
          while (hi - lo > 1){
              int mid = (hi + lo) / 2;
              if (f(mid)){
                  lo = mid;
              }
              else{
                  hi = mid;
              }
          }
  
          return lo+1;
  
      }
          
       public static void main(String[] args) {
  
              sc = new FastScanner();
              // Scanner sc = new Scanner(System.in);
              // SpecialSieve(5000000+5);
              int t = sc.nextInt();
              // sb = new StringBuilder();
              // int t = 1;
              while(t > 0){
  
                  // a = sc.nextLong();
                  n = sc.nextInt();
                  k = 2;
                  // x = sc.nextLong();
                  // m = sc.nextInt();
                  // mat = new int[2][m];
  
                  // for(int i = 0 ; i < 2 ; i++)
                  //     for(int j = 0 ; j < m ; j++)
                  //         mat[i][j] = sc.nextLong();
  
                  // for(int i = 1 ; i <= 15 ; i++){
                  //     m = i;
                  //     solve();
                  // // }
                  // board = new char[3][3];
                  // for(int i = 0 ; i < 3 ; i++){
                  //     String s = sc.next();
                  //     for(int j = 0 ; j < 3 ; j++){
                  //         board[i][j] = s.charAt(j);
                  //     }
                  // }
                  // x = sc.nextInt();
                  // ch = sc.next().toCharArray();
                  // q = sc.nextInt();
                  // ch = sc.next().toCharArray();
                  arr = new long[n];
                  for(int i = 0 ; i < n ; i++)
                      arr[i] = sc.nextLong();
  
                  a = new long[n-1];
                  for(int i = 1 ; i < n ; i++)
                      a[i-1] = Math.abs(arr[i] - arr[i-1]);
  
                  n -= 1;
  
                  System.out.println(solve());
                  t -= 1;
              }
              // System.out.print(sb);
  
       }
  
      // Use this instead of Arrays.sort() on an array of ints. Arrays.sort() is n^2
      // worst case since it uses a version of quicksort. Although this would never
      // actually show up in the real world, in codeforces, people can hack, so
      // this is needed.
      static void ruffleSort(long[] a) {
          //ruffle
          int n=a.length;
          Random r=new Random();
          for (int i=0; i<a.length; i++) {
              int oi=r.nextInt(n);long temp=a[i];
              a[i]=a[oi];
              a[oi]=temp;
          }
          
          //then sort
          Arrays.sort(a);
      }
      public static long gcd(long a, long b)
      {
        if (b == 0)
          return a;
  
        return gcd(b, a % b); 
        
      }
       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 long mod(long x, long mod)
  {
      long result = x % mod;
      if (result < 0)
      {
          result += mod;
      }
      return result;
  }
      
      // Use this to input code since it is faster than a Scanner
      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());
          }
          int[] readArray(int n) {
              int[] a=new int[n];
              for (int i=0; i<n; i++) a[i]=nextInt();
              return a;
          }
          long nextLong() {
              return Long.parseLong(next());
          }
      }
  }
  