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