from collections import defaultdict
N=int(input())
A=list(map(int,input().split()))
ma = max(A)*2
ans=0
for n in range(1,ma+1):
    dic = defaultdict(int)
    for i in range(min(ma//(n+1)+1,N)):
        d = A[i]-n*(i+1)
        ans+=dic[-d]
        dic[d] += 1
print(ans)