#include <fstream>

using namespace std;

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

int fr[7005];

int main()
{
    int n;
    fin >> n;

    for(int i = 1; i <= n; ++i)
    {
        int x;
        fin >> x;

        fr[x]++;
    }

    int rez = 0;
    for(int i = 1; i <= 7000; ++i)
    {
        if(fr[i] != 0)
            rez += (fr[i] * (fr[i] - 1) * (fr[i] - 2)) / 2;
        for(int j = i + 1; j <= 7000; ++j)
            if(fr[i] != 0 && fr[j] != 0 && (i + j) % 2 == 0)
            {
                if(fr[(i + j) / 2] != 0)
                    rez += fr[i] * fr[j] * fr[(i + j) / 2];
            }
    }
    fout << rez << '\n';
    return 0;
}