import sys,time

from itertools import permutations
from heapq import heappop,heappush
from collections import deque
import random
import bisect
from math import ceil,floor

input = lambda :sys.stdin.readline().rstrip()
mi = lambda :map(int,input().split())
li = lambda :list(mi())

M = 2*10**5

def solve(N,A):
    rest_idx = [i for i in range(N)]
    tmp_cnt = [0] * (2*M+1)
    ans = 0
    for q in range(1,2*M+1):
        nxt_idx = []
        for i in rest_idx:
            val = A[i] - q * (i+1)
            if -M <= val <= M:
                ans += tmp_cnt[M-val]
                tmp_cnt[val+M] += 1
                nxt_idx.append(i)
        for i in rest_idx:
            val = A[i] - q * (i+1)
            if -M <= val <= M:
                tmp_cnt[val+M] = 0
        rest_idx = nxt_idx
    
    return ans

N = int(input())
A = li()
print(solve(N,A))