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

int main() {
    int N; cin >> N;
    int M = 200'000;
    int A[N+1];
    for (int i = 1; i <= N; i++) cin >> A[i];
    
    vector<vector<int>> C(2*M+1);
    for (int i = 1; i <= N; i++) {
        for (int d = 1; d <= (A[i] + M) / i; d++) {
          C[d].push_back(A[i] - d * i);
        }
    }
    
    long long ans = 0;
    
    for (int d = 1; d <= (2 * M) / 3; d++) {
        unordered_map<int, int> cnt;
        for (int x : C[d]) {
        	ans += cnt[-x];
        	cnt[x]++;
        }
    }
    
    cout << ans << endl;
}