#include <bits/stdc++.h>

using namespace std;

ifstream fin("medie.in");
ofstream fout("medie.out");
int n, i, x;
int fr[7002], r, j;

int main() {
    fin >> n;
    for(i = 1; i <= n; i++) {
        fin >> x;
        fr[x]++;
    }
    for(i = 1; i <= 7000; i++) {
        for(j = i; j >= 1; j -= 2) {

            int mij = j + (i - j) / 2;

            if(i == j) r += fr[i] * (fr[i] - 1) * (fr[i] - 2) / 2;
            else r += fr[mij] * fr[i] * fr[j];
        }
    }
    fout << r;

    return 0;
}