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 D {
  	static StringBuilder sb;
  	static dsu dsu;
  	static long fact[];
  	static int mod = (int) (1e9 + 7);
  	static int si;
  	static int ei;
  
  	static void solve() {
  		int n = i();
  		long[] arr = readArray(n);
  		long[] diff = new long[n - 1];
  		if (n == 1) {
  			sb.append("1\n");
  			return;
  		}
  		for (int i = 1; i < arr.length; i++) {
  			diff[i - 1] = Math.abs(arr[i] - arr[i - 1]);
  		}
  
  		long[][] sparse = sparsetable(diff);
  
  		int i = 0;
  		int j = 0;
  		long ans = 0;
  		while (j < diff.length) {
  			int log = (int) (Math.log(j - i + 1) / Math.log(2));
  			long left = sparse[i][log];
  			long right = sparse[j - (1 << log) + 1][log];
  
  			long gcd = (gcd(left, right));
  			if (gcd > 1) {
  				ans = Math.max(ans, j - i + 1);
  				j++;
  			} else {
  				if (i < j) {
  					i++;
  				} else {
  					i++;
  					j++;
  				}
  			}
  		}
  
  		sb.append(ans + 1 + "\n");
  
  	}
  
  	static long[][] sparsetable(long[] arr) {
  		int n = arr.length;
  		int log = (int) (Math.log(n) / Math.log(2));
  		long[][] sparse = new long[arr.length][log + 1];
  		for (int i = 0; i < arr.length; i++) {
  			sparse[i][0] = arr[i];
  		}
  
  		for (int j = 1; j <= log; j++) {
  			for (int i = 0; i <= n - (1 << (j)); i++) {
  				sparse[i][j] = gcd(sparse[i][j - 1], sparse[i + (1 << (j - 1))][j - 1]);
  			}
  		}
  
  		return sparse;
  	}
  
  	static ArrayList<Integer> sieveOfEratosthenes(int n) {
  		boolean prime[] = new boolean[n + 1];
  		for (int i = 0; i <= n; i++)
  			prime[i] = true;
  
  		for (int p = 2; p * p <= n; p++) {
  			if (prime[p] == true) {
  				for (int i = p * p; i <= n; i += p)
  					prime[i] = false;
  			}
  		}
  
  		ArrayList<Integer> primes = new ArrayList<>();
  		for (int i = 2; i <= n; i++) {
  			if (prime[i] == true) {
  				primes.add(i);
  			}
  		}
  
  		return primes;
  	}
  
  	static ArrayList<Integer> primes;
  
  	public static void main(String[] args) {
  		sb = new StringBuilder();
  		int test = i();
  		primes = sieveOfEratosthenes(3020);
  		while (test-- > 0) {
  			solve();
  		}
  		System.out.println(sb);
  
  	}
  
  	static long ncr(int n, int r) {
  		if (r > n)
  			return (long) 0;
  
  		long res = fact[n] % mod;
  		res = ((long) (res % mod) * (long) (p(fact[r], mod - 2) % mod)) % mod;
  		res = ((long) (res % mod) * (long) (p(fact[n - r], mod - 2) % mod)) % mod;
  		return res;
  
  	}
  
  	static long p(long x, long y) {
  		if (y == 0)
  			return 1;
  
  		long res = 1;
  		while (y > 0) {
  			if (y % 2 == 1) {
  				res = (res * x) % mod;
  				y--;
  			}
  
  			x = (x * x) % mod;
  			y = y / 2;
  
  		}
  		return res;
  	}
  
  //**************END******************
  
  	// *************Disjoint set
  	// union*********//
  	static class dsu {
  		int parent[];
  
  		dsu(int n) {
  			parent = new int[n];
  			for (int i = 0; i < n; i++)
  				parent[i] = -1;
  		}
  
  		int find(int a) {
  			if (parent[a] < 0)
  				return a;
  			else {
  				int x = find(parent[a]);
  				parent[a] = x;
  				return x;
  			}
  		}
  
  		void merge(int a, int b) {
  			a = find(a);
  			b = find(b);
  			if (a == b)
  				return;
  			parent[b] = a;
  		}
  	}
  
  //**************PRIME FACTORIZE **********************************//
  	static TreeMap<Integer, Integer> prime(long n) {
  		TreeMap<Integer, Integer> h = new TreeMap<>();
  		long num = n;
  		for (int i = 2; i <= Math.sqrt(num); i++) {
  			if (n % i == 0) {
  				int nt = 0;
  				while (n % i == 0) {
  					n = n / i;
  					nt++;
  				}
  				h.put(i, nt);
  			}
  		}
  		if (n != 1)
  			h.put((int) n, 1);
  		return h;
  
  	}
  
  //****CLASS PAIR ************************************************
  	static class Pair implements Comparable<Pair> {
  		int x;
  		int y;
  
  		Pair(int x, int y) {
  			this.x = x;
  			this.y = y;
  		}
  
  		public int compareTo(Pair o) {
  			return (int) (this.y - o.y);
  
  		}
  
  	}
  //****CLASS PAIR **************************************************
  
  	static class InputReader {
  		private InputStream stream;
  		private byte[] buf = new byte[1024];
  		private int curChar;
  		private int numChars;
  		private SpaceCharFilter filter;
  
  		public InputReader(InputStream stream) {
  			this.stream = stream;
  		}
  
  		public int read() {
  			if (numChars == -1)
  				throw new InputMismatchException();
  			if (curChar >= numChars) {
  				curChar = 0;
  				try {
  					numChars = stream.read(buf);
  				} catch (IOException e) {
  					throw new InputMismatchException();
  				}
  				if (numChars <= 0)
  					return -1;
  			}
  			return buf[curChar++];
  		}
  
  		public int Int() {
  			int c = read();
  			while (isSpaceChar(c))
  				c = read();
  			int sgn = 1;
  			if (c == '-') {
  				sgn = -1;
  				c = read();
  			}
  			int res = 0;
  			do {
  				if (c < '0' || c > '9')
  					throw new InputMismatchException();
  				res *= 10;
  				res += c - '0';
  				c = read();
  			} while (!isSpaceChar(c));
  			return res * sgn;
  		}
  
  		public String String() {
  			int c = read();
  			while (isSpaceChar(c))
  				c = read();
  			StringBuilder res = new StringBuilder();
  			do {
  				res.appendCodePoint(c);
  				c = read();
  			} while (!isSpaceChar(c));
  			return res.toString();
  		}
  
  		public boolean isSpaceChar(int c) {
  			if (filter != null)
  				return filter.isSpaceChar(c);
  			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
  		}
  
  		public String next() {
  			return String();
  		}
  
  		public interface SpaceCharFilter {
  			public boolean isSpaceChar(int ch);
  		}
  	}
  
  	static class OutputWriter {
  		private final PrintWriter writer;
  
  		public OutputWriter(OutputStream outputStream) {
  			writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
  		}
  
  		public OutputWriter(Writer writer) {
  			this.writer = new PrintWriter(writer);
  		}
  
  		public void print(Object... objects) {
  			for (int i = 0; i < objects.length; i++) {
  				if (i != 0)
  					writer.print(' ');
  				writer.print(objects[i]);
  			}
  		}
  
  		public void printLine(Object... objects) {
  			print(objects);
  			writer.println();
  		}
  
  		public void close() {
  			writer.close();
  		}
  
  		public void flush() {
  			writer.flush();
  		}
  	}
  
  	static InputReader in = new InputReader(System.in);
  	static OutputWriter out = new OutputWriter(System.out);
  
  	public static long[] sort(long[] a2) {
  		int n = a2.length;
  		ArrayList<Long> l = new ArrayList<>();
  		for (long i : a2)
  			l.add(i);
  		Collections.sort(l);
  		for (int i = 0; i < l.size(); i++)
  			a2[i] = l.get(i);
  		return a2;
  	}
  
  	public static int[] sort(int[] a2) {
  		int n = a2.length;
  		ArrayList<Integer> l = new ArrayList<>();
  		for (int i : a2)
  			l.add(i);
  		Collections.sort(l);
  		for (int i = 0; i < l.size(); i++)
  			a2[i] = l.get(i);
  		return a2;
  	}
  
  	public static long pow(long x, long y) {
  		long res = 1;
  		while (y > 0) {
  			if (y % 2 != 0) {
  				res = (res * x);// % modulus;
  				y--;
  
  			}
  			x = (x * x);// % modulus;
  			y = y / 2;
  		}
  		return res;
  	}
  
  //GCD___+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
  	public static long gcd(long x, long y) {
  		if (x == 0)
  			return y;
  		else
  			return gcd(y % x, x);
  	}
  	// ******LOWEST COMMON MULTIPLE
  	// *********************************************
  
  	public static long lcm(long x, long y) {
  		return (x * (y / gcd(x, y)));
  	}
  
  //INPUT PATTERN********************************************************
  	public static int i() {
  		return in.Int();
  	}
  
  	public static long l() {
  		String s = in.String();
  		return Long.parseLong(s);
  	}
  
  	public static String s() {
  		return in.String();
  	}
  
  	public static int[] readArrayi(int n) {
  		int A[] = new int[n];
  		for (int i = 0; i < n; i++) {
  			A[i] = i();
  		}
  		return A;
  	}
  
  	public static long[] readArray(long n) {
  		long A[] = new long[(int) n];
  		for (int i = 0; i < n; i++) {
  			A[i] = l();
  		}
  		return A;
  	}
  
  }