#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    constexpr int r = 400000;
    vector<int> A(2 * r + 1);
    auto cnt = A.begin() + r;
    int n;
    cin >> n;
    vector<int> a(n);
    for(auto &&v : a) cin >> v;
    auto b = a.begin() - 1;
    ll ans = 0;
    for(int d = 1; d <= 200000; d++){
        int m = min(n, 200000 / d);
        for(int i = 1; i <= m; i++){
            int lv = b[i] - i * d;
            if(-r <= lv && lv <= r){
                ans += cnt[-lv];
                cnt[lv]++;
            }
        }
        for(int i = 1; i <= m; i++){
            int lv = b[i] - i * d;
            if(-r <= lv && lv <= r) cnt[lv]--;
        }
    }
    cout << ans << '\n';
}