from collections import defaultdict

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

lim = 400010

ans = 0
cnt = defaultdict(int)
for i in range(1, n + 1):
    for k in range(1, lim//i + 1):
        ans += cnt[(k, k * i - a[i-1])]
        cnt[(k, a[i-1] - k * i)] += 1

print(ans)