N = int(input())
A = list(map(int, input().split()))
M = 2001

cnt = [[0] * M for _ in range(M)]

ans = 0
for i in range(N):
    for j in range(i):
        k = A[i] - A[j] - 1
        if k <= 0:
            continue
        a2 = A[j] + k
        a1 = a2 - (k + 10)
        if 1 <= a1 < M and 1 <= a2 < M:
            ans += cnt[a1][a2]
    for j in range(i):
        cnt[A[j]][A[i]] += 1

print(ans)