N = int(input())
A = list(map(int, input().split()))
d = {}
for i, a in enumerate(A):
    if a in d:
        d[a].append(i)
    else:
        d[a] = [i]
ans = 0
for k in range(1, 2000):
    for i in d:
        tmp = []
        a = [i, 0, 0, 0]
        a[1] = a[0]+(k+10)
        a[2] = a[1]-k
        a[3] = a[2]+(k+1)
        if not all(a[j] in d for j in range(1, 4)):
            continue
        for x in range(4):
            for j in d[a[x]]:
                tmp.append((j, x))
        tmp.sort()
        dp = [1, 0, 0, 0, 0]
        for j, x in tmp:
            dp[x+1] += dp[x]
        # print(tmp)
        # print(dp)
        ans += dp[-1]
print(ans)