from collections import defaultdict
from bisect import bisect_left, bisect_right

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, (2 * M) // 3 + 1):
	C[d].sort()
	cnt0 = 0
	for c in C[d]:
		if c > 0:
			break
		elif c == 0:
			cnt0 += 1
		else:
			ans += bisect_right(C[d], -c) - bisect_left(C[d], -c)
	ans += cnt0 * (cnt0 - 1) // 2
print(ans)