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

int N;

int solve1(vector<int> A){
  int B = 447;
  int ans = 0;
  for(int i = 1; i <= 3*B; i++){
  	for(int j = i + 1; j <= 3*B; j++){
  		if(i >= N || j >= N) continue;
  		if((A[i] + A[j]) % (i + j) == 0){
  			ans++;
  			if((A[i] + A[j]) / (i + j) <= B){
  				ans--;
  			}
  		}
  	}
  }
  vector<int> cnt(600000);
  int ho = 300000;
  for(int i = 1; i <= B; ++i){
  	for(int j = 1; j <= N; ++j){
  	  if((j * i) - A[j] + ho < 600000){
  	    ans += cnt[(j * i) - A[j] + ho];
  	  }
  	  if(A[j] - (j * i) + ho >= 0){
  	    cnt[A[j] - (j * i) + ho]++;
  	  }
  	}
  	for(int j = 1; j <= N; ++j){
  	  if(A[j] - (j * i) + ho >= 0){
  	    cnt[A[j] - (j * i) + ho]--;
  	  }
  	}
  }
  return ans;
}

int solve2(vector<int> A){
  int ans = 0;
  for(int i = 1; i <= N; i++){
    for(int j = i + 1; j <= N; j++){
      if((A[i]+A[j]) % (i+j) == 0){
        ans++;
      }
    }
  }
  return ans;
}

signed main(){
  cin>>N;
  vector<int> A(N+1);
  for(int i = 1; i <= N; i++) cin>>A[i];
  cout << solve1(A) << "\n";
}