def solve(A):
   N = len(A)
   U = max(A)
   T = int((U*U//N//10)**(1/3)) + 1

   from collections import defaultdict
   res = 0
   for k in range(1, T+1):
      d = defaultdict(int)
      for i, a in enumerate(A, 1):
         key = a - k*i
         res += d[-(key)]
         d[key] += 1

   mx = (2*U)//T
   for i, a in enumerate(A, 1):
      if not (i <= mx): break
      for j, b in enumerate(A, 1):
         if not (i+j <= mx): break
         if not (i < j): continue
         if (a+b) % (i+j) != 0: continue
         k = (a+b) // (i+j)
         if (T+1 <= k):
            res += 1
   return res


N = int(input())
A = list(map(int, input().split()))
ans = solve(A)
print(ans)