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

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    constexpr int r = 200000;
    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 <= 133333; d++){
        int m = min(n, r / d  * 2);
        for(int i = 1; i <= m; i++){
            b[i] -= i;
            if(-r <= b[i] && b[i] <= r){
                ans += cnt[-b[i]];
                cnt[b[i]]++;
            }
        }
        for(int i = 1; i <= m; i++){
            if(-r <= b[i] && b[i] <= r) cnt[b[i]]--;
        }
    }
    cout << ans << '\n';
}