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.io.*;
  public class Solution{ 
  	
  	 static void fun(long ST[][],int n,int k,long a[]){
           for (int i = 0; i <n; i++)
                ST[i][0] = a[i];
            
           for (int j = 1; j <k; j++)
              for (int i = 0; (i+(1 << j))<=n; i++)
                      ST[i][j] = gcd(ST[i][j-1], ST[i + (1 << (j - 1))][j - 1]);
   } 
  	 static long query(int l,int r) {
  		 int j=Log[r-l+1];
           long g = gcd(ST[l][j],ST[r-(1<<j)+1][j]);
           return g;
  	 }
  	 static long[][] ST;
  	 static int[] Log;
  	 static boolean ok(int l,int n) {
  		 int i1=0,i2=l-1;
  		 while(i2<n) {
  			 long g = query(i1,i2);
  			 if(g>1)
  				 return true;
  			 i1++;i2++;
  		 }
  		 return false;
  	 }
  public static void main(String[] args)throws Exception
  {  
  	//System.out.println("enter a number");
  
  
  int t = ni();
  for(int u=1;u<=t;u++) {
    
  	int n = ni();
      long a[] = al(n);
      if(n==1)
      	out.println(1);
      else {
      	long d[] = new long[n-1];
      	for(int i=1;i<n;i++)
      		d[i-1]=Math.abs(a[i]-a[i-1]);
      	 int k = (int)(Math.log(n-1)/Math.log(2))+1;
            ST = new long[n-1][k];
           Log = new int[n];
  
               fun(ST,n-1,k,d);
               Log[1] = 0;
              for (int i = 2; i <n; i++)
                    Log[i] = Log[i/2]+1;
      	int l=0,r=n;
      	while((r-l)>1) {
      		int m=(l+r)/2;
      		if(ok(m,n-1))
      		  l=m;
      		else
      		  r=m;
      	}
      	l=l+1;
      	out.println(l);
      }
  }
       out.flush();
  }
  static HashMap<Integer,Integer> gethm(int a[]){
  	 HashMap<Integer,Integer> hm = new HashMap();
  	 for(int i=0;i<a.length;i++)
  		 if(hm.containsKey(a[i]))
  			 hm.put(a[i], hm.get(a[i])+1);
  		 else
  			 hm.put(a[i], 1);
  	 return hm;
  }
  ////////////////////////// solution ends ////////////////////////////////////////////////
  static class pair
  	{
  		int l,k;
  		pair(){}
  		pair(int c,int d){l=c;k=d;}
  		/*@Override
  		public int hashCode(){return (a+" "+b).hashCode();}
  		@Override public boolean equals(Object c){if(a==((pair)c).a&&b==((pair)c).b)return true;return false;} */
  	}  
  static void seive(boolean p[]){
  
                      p[0]=true; p[1]=true;
                  for(int i=2;i*i<p.length;i++)
                     if(p[i]==false){
                      for(int j=i*i;j<p.length;j=j+i)
                           p[j]=true;
                    }
               }
  static int get(int index)
          {
                  return (index&(-index));
          }
  static void add(int bit[],int index,int val)
          {
               while(index<bit.length)
                 {
                      bit[index] = bit[index]+val;
                      index = index + get(index);
                 }
          }
  static int get(int bit[],int index)
           {
                 int sum=0;
                 while(index>0)
                  {
                      sum = sum+bit[index];
                      index = index-get(index);
                  }
                return sum;
           }
  static void add(long bit[],int index,long val)
          {
               while(index<bit.length)
                 {
                      bit[index] = bit[index]+val;
                      index = index + get(index);
                 }
          }
  static long get(long bit[],int index)
           {
                 long sum=0;
                 while(index>0)
                  {
                      sum = sum+bit[index];
                      index = index-get(index);
                  }
                return sum;
           } 
  static void compress(int a[])
           {      
                  int n = a.length;
                  Integer ar[] = new Integer[n];
                  for(int i=0;i<n;i++)
                       ar[i] = a[i];
                  Arrays.sort(ar);
                  HashMap<Integer,Integer> hm = new HashMap();
                  int st=1;
                  for(int i=0;i<n;i++)
                      if(!hm.containsKey(ar[i]))
                          hm.put(ar[i],st++);
                  for(int i=0;i<n;i++)
                     a[i] = hm.get(a[i]);
           }
  static int find(int x,int p[]){ if(x==p[x]) return x; return p[x]=find(p[x],p) ;}
  static void union(int x,int y,int p[]){ int xr=find(x,p),yr=find(y,p); if(xr!=yr){ p[xr]=yr;} }
   
  static int abs(int x){ return x>0 ? x : -x; }
  static long abs(long x){ return x>0 ? x : -x; }
  static long gcd(long a,long b){ if(a==0)return b; if(b==0) return a;if(b%a==0) return a;return gcd(b%a,a); }
  static int gcd(int a,int b){ if(a==0)return b; if(b==0) return a; if(b%a==0) return a;return gcd(b%a,a); }
  static long min(long a,long b){ return a<b ? a : b; }
  static int min(int a,int b){ return a<b ? a : b; }
  static long max(long a,long b){ return a>b ? a : b; }
  static int max(int a,int b){ return a>b ? a : b; }
  static long pow(long a,long b,long md){ long ans=1;  while(b>0){if(b%2==1) ans = (ans*a)%md; a = (a*a)%md; b = b/2;} return ans; }
  static int log2n(long a){ int te=0; while(a>0) {a>>=1; ++te; } return te; }
  
  static void reverse(int a[]){int i1=0,i2=a.length-1; while(i1<i2){int t = a[i1];a[i1]=a[i2];a[i2]=t;i1++;i2--;}  } 
  static void reverse(long a[]){ int i1=0,i2=a.length-1; while(i1<i2){ long t = a[i1]; a[i1]=a[i2];a[i2]=t;i1++;i2--;}  } 
  
  static void subtract_1(char s[]){if(s[0]=='0') return;int n = s.length,i=n-1;while(s[i]=='0')i--;s[i] =(char)((int)(s[i]-'0') + 47);for(int j=i+1;j<n;j++)s[j]='9';}
  static void reverse(char s[]){int i1=0,i2=s.length-1; while(i1<i2){char t=s[i1];s[i1]=s[i2];s[i2]=t; i1++;i2--;} }
  static String reverse(String r){String s = "";int i= r.length()-1; while(i>=0){ s=s+r.charAt(i);i--;}return s;}
  static boolean pal(char s[]){ int i1=0,i2=s.length-1; while(i1<i2){ if(s[i1]!=s[i2]) return false; i1++;i2--;} return true;}
  static boolean pal(String s){int n = s.length(),i1=0,i2=n-1;while(i1<i2){if(s.charAt(i1)!=s.charAt(i2))return false;i1++; i2--;}return true;}
   
  // Input OutPut Functions
  static PrintWriter out = new PrintWriter(System.out);
  static FastReader sc=new FastReader();
  static int ni(){ int x = sc.nextInt();return(x); }
  static long nl(){ long x = sc.nextLong(); return(x); }
  
  static String n(){ String str = sc.next(); return(str); }
  static String ns(){ String str = sc.nextLine(); return(str);}
  static double nd(){double d = sc.nextDouble(); return(d); }
  static int[] ai(int n){ int a[] = new int[n]; for(int i=0;i<n;i++) a[i] = ni(); return a; }
  static long[] al(int n) {long a[] = new long[n]; for(int i=0;i<n;i++) a[i] = nl(); return a; }
  static double[] ad(int n) { double a[]= new double[n]; for(int i=0;i<n;i++) a[i]=nd(); return a;} 
  static String[] as(int n){ String a[] = new String[n]; for(int i=0;i<n;i++) a[i] = n(); return a; }
  static void p(Object o){ out.print(o); }
  static void pn(Object o){ out.println(o); } 
   
  static class FastReader{ 
  BufferedReader br; 
  StringTokenizer st;   
  public FastReader() { br = new BufferedReader(new InputStreamReader(System.in));  }   
  String next(){while(st==null || !st.hasMoreElements()){try{st = new StringTokenizer(br.readLine());}catch (IOException  e){e.printStackTrace();}}return st.nextToken();} 
  int nextInt(){ return Integer.parseInt(next()); } 
  long nextLong(){ return Long.parseLong(next()); } 
  double nextDouble(){return Double.parseDouble(next()); } 
  String nextLine(){ String str = ""; try{ str = br.readLine();} catch (IOException e){ e.printStackTrace();} return str;} 
    } 
  }