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

int main(){
  using ll=long long;
  int m=4e5;
  int n;
  cin>>n;
  vector<int> a(n);
  for (int i=0;i<n;i++) cin>>a[i];
  ll ans=0;
  map<pair<int,int>,int> mp;
  for (int i=0;i<n;i++){
    for (int j=0;j*(i+1)<=m;j++){
      ll val=a[i]-(i+1)*j;
      ans+=mp[{j,-val}];
      mp[{j,val}]++;
    }
  }
  cout<<ans<<endl;
}