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 sys
  import math
  input = sys.stdin.readline
  INF = 10**20
  def gcd(a, b):
      if a == INF:
          return b
      if b == INF:
          return a
      return math.gcd(a, b)
  class LazySegmentTree:
      def __init__(self, data, default=0, func=min):
          """initialize the lazy segment tree with data"""
          self._default = default
          self._func = func
  
          self._len = len(data)
          self._size = _size = 1 << (self._len - 1).bit_length()
          self._lazy = [0] * (2 * _size)
  
          self.data = [default] * (2 * _size)
          self.data[_size:_size + self._len] = data
          for i in reversed(range(_size)):
              self.data[i] = func(self.data[i + i], self.data[i + i + 1])
  
      def __len__(self):
          return self._len
  
      def _push(self, idx):
          """push query on idx to its children"""
          # Let the children know of the queries
          q, self._lazy[idx] = self._lazy[idx], 0
  
          self._lazy[2 * idx] += q
          self._lazy[2 * idx + 1] += q
          self.data[2 * idx] += q
          self.data[2 * idx + 1] += q
  
      def _update(self, idx):
          """updates the node idx to know of all queries applied to it via its ancestors"""
          for i in reversed(range(1, idx.bit_length())):
              self._push(idx >> i)
  
      def _build(self, idx):
          """make the changes to idx be known to its ancestors"""
          idx >>= 1
          while idx:
              self.data[idx] = self._func(self.data[2 * idx], self.data[2 * idx + 1]) + self._lazy[idx]
              idx >>= 1
  
      def add(self, start, stop, value):
          """lazily add value to [start, stop)"""
          start = start_copy = start + self._size
          stop = stop_copy = stop + self._size
          while start < stop:
              if start & 1:
                  self._lazy[start] += value
                  self.data[start] += value
                  start += 1
              if stop & 1:
                  stop -= 1
                  self._lazy[stop] += value
                  self.data[stop] += value
              start >>= 1
              stop >>= 1
  
          # Tell all nodes above of the updated area of the updates
          self._build(start_copy)
          self._build(stop_copy - 1)
  
      def query(self, start, stop, default=1e9):
          """func of data[start, stop)"""
          start += self._size
          stop += self._size
  
          # Apply all the lazily stored queries
          self._update(start)
          self._update(stop - 1)
  
          res = default
          while start < stop:
              if start & 1:
                  res = self._func(res, self.data[start])
                  start += 1
              if stop & 1:
                  stop -= 1
                  res = self._func(res, self.data[stop])
              start >>= 1
              stop >>= 1
          return res
  
      def __repr__(self):
          return "LazySegmentTree({0})".format(self.data)
  
  t = int(input())
  for _ in range(t):
      n = int(input())
      s = list(map(int, input().split()))
      s = [abs(s[i]-s[i+1]) for i in range(n-1)] + [1]
      N = len(s)
      T = LazySegmentTree(s, func=gcd)
      ans = 1
      for l in range(n - 1):
          r = l + ans
          if r >= n:
              break
          g = T.query(l, r, default=INF)
          # dbp('queried:', difflist[l:r], 'got:', g)
          if g == 1:
              continue
  
          while r < n and g > 1:
              # dbp('checking:', g, difflist[r])
              g = gcd(g, s[r])
              r += 1
  
          ans = max(ans, r - l)
      print(ans)
  