N = int(input())
A = list(map(int, input().split()))
maxa = max(A)
ans = 0

for k in range(1, maxa):
    dp = [[0] * (maxa + 1) for _ in range(5)]
    dp[0][0] = 1
    for a in A:
        dp[1][a] += dp[0][0]
        if 0 < a - k - 10 <= maxa:
            dp[2][a] += dp[1][a - k - 10]
        if 0 < a + k <= maxa:
            dp[3][a] += dp[2][a + k]
        if 0 < a - k - 1 <= maxa:
            dp[4][a] += dp[3][a - k - 1]
    ans += sum(dp[4])
print(ans)