from collections import defaultdict
N = int(input())
M = 200000
A = list(map(int, input().split()))

C = [[] for i in range(2*M+1)]

for i in range(N):
	for d in range(1, (A[i] + M) // (i+1) + 1):
		C[d].append(A[i] - (i+1) * d)

ans = 0
for d in range(1, M+1):
	cnt = defaultdict(int)
	for c in C[d]:
		ans += cnt[-c]
		cnt[c] += 1
print(ans)