from collections import defaultdict
N = int(input())
A = list(map(int,input().split()))
D = defaultdict(int)
ans = 0
for i in range(1,N-2):
  D[A[i-1]] += 1
  dd = defaultdict(int)
  for j in range(i+1,N):
    dd[A[j]] += 1
  for j in range(i+1,N-1):
    dd[A[j]] -= 1
    b = A[i]
    c = A[j]
    k = b - c
    a = b - k - 10
    d = c + k + 1
    ans += D[a]*dd[d]
print(ans)