#include <bits/stdc++.h>
#pragma GCC optimize ("Ofast")

using namespace std;

ifstream fin  ("medie.in");
ofstream fout ("medie.out");

const int LIM = 7000;
int n, x, freq[LIM + 5];
long long sol;

int main (){
    ios_base::sync_with_stdio(false);
    fin.tie(nullptr);
    fout.tie(nullptr);

    fin>>n;
    for(int i=1; i<=n; i++){
        fin>>x;
        freq[x]++;
    }

    for(int i=1; i<=LIM; i++){
        sol += (long long)freq[i] * (freq[i]-1) * (freq[i]-2) / 2;
        for(int dif=1; 1<=i-dif && i+dif<=LIM; dif++)
            sol += (long long)freq[i] * freq[i-dif] * freq[i+dif];
    }
    fout<<sol;
    return 0;
}