#include <bits/stdc++.h>
#define PLEC fin.close(); fout.close(); return 0;
using namespace std;
ifstream fin("medie.in");
ofstream fout("medie.out");
const int N(7000);
int freq[N + 5], n, x, res;
int main()
{
    fin >> n;
    for (int i = 1; i <= n; ++i)
        fin >> x, ++freq[x];
    for (int i = 1; i <= N; ++i)
    {
        res += freq[i] * (freq[i] - 1) * (freq[i] - 2) / 2;
        for (int j = 1; j < i; ++j)
            if (2 * i - j <= N)
                res += freq[j] * freq[i] * freq[2 * i - j];
    }
    fout << res;
    PLEC
}