from collections import defaultdict

n = int(input())
a = list(map(int, input().split(' ')))

ans = 0

for d in range(1,1000):
    dp = [[0 for j in range(4)] for i in range(n)]
    mp = defaultdict(int)
    for i in range(n):
        dp[i][0] += 1
        dp[i][1] += mp[(a[i] - 10 - d, 0)]
        dp[i][2] += mp[(a[i] + d, 1)]
        dp[i][3] += mp[(a[i] - d - 1, 2)]
        for j in range(4):
            mp[(a[i], j)] += dp[i][j]
        ans += dp[i][3]
print(ans)