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.io.BufferedReader;
  import java.io.FileReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.util.StringTokenizer;
  import java.util.Arrays;
  import java.util.Random;
  import java.io.FileWriter;
  import java.io.PrintWriter;
  /*
      Solution Created: 23:38:00 01/08/2021
      Custom Competitive programming helper.
  */
  public class Main {
  	static int n;
  	static long[] a;
  	static SegmentTree st;
  	public static void solve() {
  		n = in.nextInt();
  		a = in.nl(n);
  		if(n==1) {
  			out.println(1);
  			return;
  		}
  		long[] diff = new long[n-1];
  		for(int i = 0; i<n-1; i++) diff[i] = Math.abs(a[i+1]-a[i]);
  		st = new SegmentTree(diff);
  		int ans = 1, j = 0;
  		for(int i = 0; i<n; i++) {
  			j = Math.max(i, j);
  			while(j+1<n && st.query(i, j)>=2) j++;
  			ans = Math.max(ans, j-i+1);
  		}
  		out.println(ans);
  	}
  	
  	static boolean can(int sz) {
  		for(int i = 0; i+sz-1<n; i++) if(st.query(i, i+sz-2)>=2) return true;
  		return false;
  	}
  	
  	static class SegmentTree{
  		int dummyValue = 0;
  		public long operation(long a, long b){
  			return Util.gcd(a, b);
  		}
  		private long[] tree;
  		int n;
  		public SegmentTree(long[] diff) {
  			this.n = diff.length;
  			this.tree = new long[4*n];
  			build(0, 0, n-1, diff);
  		}
  		
  		public SegmentTree(int n) {
  			this.n = n;
  			this.tree = new long[4*n];
  		}
  		
  		private void build(int idx, int l, int r, long[] a) {
  			if(l==r) tree[idx] = a[l];
  			else {
  				int m = (l+r)/2;
  				build(2*idx+1, l, m, a);
  				build(2*idx+2,m+1,r, a);
  				tree[idx] = operation(tree[2*idx+1], tree[2*idx+2]);
  			}
  		}
  		
  		public void update(int idx, long weight) {
  			updateUtil(0, 0, n-1, idx, weight);
  		}
  		
  		private void updateUtil(int idx ,int l, int r, int i, long weight) {
  			if(l==r) tree[idx] = weight;
  			else {
  				int md = (l+r)/2;
  				if(i<=md) updateUtil(2*idx+1, l, md, i, weight);
  				else updateUtil(2*idx+2, md+1, r, i, weight);
  				tree[idx] = operation(tree[2*idx+1], tree[2*idx+2]);
  			}
  		}
  		
  		public long query(int l, int r) {
  			return queryUtil(0, l, r, 0, n-1);
  		}
  		
  		private long queryUtil(int idx, int lBound, int rBound, int l, int r) {
  			if(rBound < l || r < lBound) return dummyValue;
  			if(lBound <= l && r<= rBound) return tree[idx];
  			int md = (l+r)/2;
  			return operation(queryUtil(2*idx+1, lBound, rBound, l, md), queryUtil(2*idx+2, lBound, rBound, md+1, r));
  		}
  	}
  	public static void main(String[] args) {
  		in = new Reader();
  		out = new Writer();
  		int t = in.nextInt();
  		while(t-->0) solve();
  		out.exit();
  	}
  	static Reader in; static Writer out;
  
  static class Reader {
  	static BufferedReader br;
  	static StringTokenizer st;
  	
  	public Reader() {
  		this.br = new BufferedReader(new InputStreamReader(System.in));
  	}
  	
  	public Reader(String f){
  		try {
  			this.br = new BufferedReader(new FileReader(f));
  		} catch (IOException e) {
  			e.printStackTrace();
  		}
  	}
  	
  	public int[] na(int n) {
  		int[] a = new int[n];
  		for (int i = 0; i < n; i++) a[i] = nextInt();
  		return a;
  	}
  
  	public double[] nd(int n) {
  		double[] a = new double[n];
  		for (int i = 0; i < n; i++) a[i] = nextDouble();
  		return a;
  	}
  	
  	public long[] nl(int n) {
  		long[] a = new long[n];
  		for (int i = 0; i < n; i++) a[i] = nextLong();
  		return a;
  	}
  
  	public char[] nca() {
  		return next().toCharArray();
  	}
  
  	public String[] ns(int n) {
  		String[] a = new String[n];
  		for (int i = 0; i < n; i++) a[i] = next();
  		return a;
  	}
  
  	public int nextInt() {
  		ensureNext();
  		return Integer.parseInt(st.nextToken());
  	}
  
  	public double nextDouble() {
  		ensureNext();
  		return Double.parseDouble(st.nextToken());
  	}
  
  	public Long nextLong() {
  		ensureNext();
  		return Long.parseLong(st.nextToken());
  	}
  
  	public String next() {
  		ensureNext();
  		return st.nextToken();
  	}
  	
  	public String nextLine() {
  		try {
  			return br.readLine();
  		} catch (Exception e) {
  			e.printStackTrace();
  			return null;
  		}
  	}
  	
  	private void ensureNext() {
  		if (st == null || !st.hasMoreTokens()) {
  			try {
  				st = new StringTokenizer(br.readLine());
  			} catch (IOException e) {
  				e.printStackTrace();
  			}
  		}
  	}
  }
  
  static class Util{
  		private static Random random = new Random();
  		static long[] fact;
  		
  		public static void initFactorial(int n, long mod) {
  			fact = new long[n+1];
  			fact[0] = 1;
  			for (int i = 1; i < n+1; i++) fact[i] = (fact[i - 1] * i) % mod;
  		}
  		
  		public static long modInverse(long a, long MOD) {
  			long[] gcdE = gcdExtended(a, MOD);
  			if (gcdE[0] != 1) return -1; // Inverted doesn't exist
  			long x = gcdE[1];
  			return (x % MOD + MOD) % MOD;
  		}
  		
  		public static long[] gcdExtended(long p, long q) {
  			if (q == 0) return new long[] { p, 1, 0 };
  			long[] vals = gcdExtended(q, p % q);
  			long tmp = vals[2];
  			vals[2] = vals[1] - (p / q) * vals[2];
  			vals[1] = tmp;
  			return vals;
  		}
  		
  		public static long nCr(int n, int r, long MOD) {
  			if (r == 0) return 1;
  			return (fact[n] * modInverse(fact[r], MOD) % MOD * modInverse(fact[n - r], MOD) % MOD) % MOD;
  		}
  		
  		public static long nCr(int n, int r) {
  			return (fact[n]/fact[r])/fact[n-r];
  		}
  		
  		public static long nPr(int n, int r, long MOD) {
  			if (r == 0) return 1;
  			return (fact[n] * modInverse(fact[n - r], MOD) % MOD) % MOD;
  		}
  		public static long nPr(int n, int r) {
  			return fact[n]/fact[n-r];
  		}
  		
  		public static boolean isPrime(int n) { 
  	        if (n <= 1) return false; 
  	        if (n <= 3) return true; 
  	        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 boolean[] getSieve(int n) {
  	        boolean[] isPrime = new boolean[n+1];
  	        for (int i = 2; i <= n; i++) isPrime[i] = true;
  	        for (int i = 2; i*i <= n; i++) if (isPrime[i]) 
  	                for (int j = i; i*j <= n; j++) isPrime[i*j] = false;
  	        return isPrime;
  	    }
  	    
  	    public static int gcd(int a, int b) { 
  	    	int tmp = 0;
  	    	while(b != 0) {
  	    		tmp = b;
  	    		b = a%b;
  	    		a = tmp;
  	    	}
  	    	return a;
  	    }
  	    
  	    public static long gcd(long a, long b) { 
  	    	long tmp = 0;
  	    	while(b != 0) {
  	    		tmp = b;
  	    		b = a%b;
  	    		a = tmp;
  	    	}
  	    	return a;
  	    }
  	    
  	    public static int random(int min, int max) {
  	    	return random.nextInt(max-min+1)+min;
  	    }
  	    
  		public static void dbg(Object... o) { 
  			System.out.println(Arrays.deepToString(o)); 
  		}
  		
  		public static void reverse(int[] s, int l , int r) {
  			for(int i = l; i<=(l+r)/2; i++) {
  				int tmp = s[i];
  				s[i] = s[r+l-i];
  				s[r+l-i] = tmp;
  			}
  	    }
  		
  		public static void reverse(int[] s) {
  			reverse(s, 0, s.length-1);
  	    }
  		
  		public static void reverse(long[] s, int l , int r) {
  			for(int i = l; i<=(l+r)/2; i++) {
  				long tmp = s[i];
  				s[i] = s[r+l-i];
  				s[r+l-i] = tmp;
  			}
  	    }
  		
  		public static void reverse(long[] s) {
  			reverse(s, 0, s.length-1);
  	    }
  		
  		public static void reverse(float[] s, int l , int r) {
  			for(int i = l; i<=(l+r)/2; i++) {
  				float tmp = s[i];
  				s[i] = s[r+l-i];
  				s[r+l-i] = tmp;
  			}
  	    }
  		
  		public static void reverse(float[] s) {
  			reverse(s, 0, s.length-1);
  	    }
  		
  		public static void reverse(double[] s, int l , int r) {
  			for(int i = l; i<=(l+r)/2; i++) {
  				double tmp = s[i];
  				s[i] = s[r+l-i];
  				s[r+l-i] = tmp;
  			}
  	    }
  		
  		public static void reverse(double[] s) {
  			reverse(s, 0, s.length-1);
  	    }
  		
  		public static void reverse(char[] s, int l , int r) {
  			for(int i = l; i<=(l+r)/2; i++) {
  				char tmp = s[i];
  				s[i] = s[r+l-i];
  				s[r+l-i] = tmp;
  			}
  	    }
  		
  		public static void reverse(char[] s) {
  			reverse(s, 0, s.length-1);
  	    }
  		
  		public static <T> void reverse(T[] s, int l , int r) {
  			for(int i = l; i<=(l+r)/2; i++) {
  				T tmp = s[i];
  				s[i] = s[r+l-i];
  				s[r+l-i] = tmp;
  			}
  	    }
  		
  		public static <T> void reverse(T[] s) {
  			reverse(s, 0, s.length-1);
  	    }
  		
  		public static void shuffle(int[] s) {
  	        for (int i = 0; i < s.length; ++i) {
  	            int j = random.nextInt(i + 1);
  	            int t = s[i];
  	            s[i] = s[j];
  	            s[j] = t;
  	        }
  	    }
  		
  	    public static void shuffle(long[] s) {
  	        for (int i = 0; i < s.length; ++i) {
  	            int j = random.nextInt(i + 1);
  	            long t = s[i];
  	            s[i] = s[j];
  	            s[j] = t;
  	        }
  	    }
  	    
  	    public static void shuffle(float[] s) {
  	        for (int i = 0; i < s.length; ++i) {
  	            int j = random.nextInt(i + 1);
  	            float t = s[i];
  	            s[i] = s[j];
  	            s[j] = t;
  	        }
  	    }
  	    
  	    public static void shuffle(double[] s) {
  	        for (int i = 0; i < s.length; ++i) {
  	            int j = random.nextInt(i + 1);
  	            double t = s[i];
  	            s[i] = s[j];
  	            s[j] = t;
  	        }
  	    }
  	    
  	    public static void shuffle(char[] s) {
  	        for (int i = 0; i < s.length; ++i) {
  	            int j = random.nextInt(i + 1);
  	            char t = s[i];
  	            s[i] = s[j];
  	            s[j] = t;
  	        }
  	    }
  	    
  	    public static <T> void shuffle(T[] s) {
  	        for (int i = 0; i < s.length; ++i) {
  	            int j = random.nextInt(i + 1);
  	            T t = s[i];
  	            s[i] = s[j];
  	            s[j] = t;
  	        }
  	    }
  	    
  		public static void sortArray(int[] a) {
  	        shuffle(a);
  	        Arrays.sort(a);
  	    }
  		
  		public static void sortArray(long[] a) {
  			shuffle(a);
  	        Arrays.sort(a);
  	    }
  		
  		public static void sortArray(float[] a) {
  			shuffle(a);
  	        Arrays.sort(a);
  	    }
  		
  		public static void sortArray(double[] a) {
  			shuffle(a);
  	        Arrays.sort(a);
  	    }
  		
  		public static void sortArray(char[] a) {
  			shuffle(a);
  	        Arrays.sort(a);
  	    }
  		
  		public static <T extends Comparable<T>> void sortArray(T[] a) {
  	        Arrays.sort(a);
  	    }
  	}
  
  static class Writer {
  	private PrintWriter pw;
  	public Writer(){
  		pw = new PrintWriter(System.out);
  	}
  	
  	public Writer(String f){
  		try {
  			pw = new PrintWriter(new FileWriter(f));
  		} catch (IOException e) {
  			e.printStackTrace();
  		}
  	}
  	
  	public void yesNo(boolean condition) {
  		println(condition?"YES":"NO");
  	}
  	
  	public void printArray(int[] a) {
  		for(int i = 0; i<a.length; i++) print(a[i]+" ");
  	}
  	
  	public void printlnArray(int[] a) {
  		for(int i = 0; i<a.length; i++) print(a[i]+" ");
  		pw.println();
  	}
  	
  	public void printArray(long[] a) {
  		for(int i = 0; i<a.length; i++) print(a[i]+" ");
  	}
  	
  	public void printlnArray(long[] a) {
  		for(int i = 0; i<a.length; i++) print(a[i]+" ");
  		pw.println();
  	}
  	
  	public void print(Object o) {
  		pw.print(o.toString());
  	}
  	
  	public void println(Object o) {
  		pw.println(o.toString());
  	}
  	
  	public void println() {
  		pw.println();
  	}
  	
  	public void flush() {
  		pw.flush();
  	}
  	public void exit() {
  		pw.close();
  	}
  }
  }
  