#include <fstream>

using namespace std;

ifstream f("medie.in");
ofstream g("medie.out");

int fr[7001], v[9001], n;

int main ()
{
    int i, j, aux, maxc;
    maxc = 0;
    long rez = 0;
    f >> n;
    for(i = 0; i < n; ++i)
    {
        f >> aux;
        ++fr[aux];
        if(aux > maxc)
            maxc = aux;
    }
    for(i = 1; i <= maxc; ++i)
    {
        if(fr[i])
            for(j = i + 1; j <= maxc; ++j)
                if(fr[i] && fr[(i + j) / 2])
                    rez += fr[i] * fr[j] * fr[(i + j) / 2];
        if(fr[i] >= 3)
            rez += fr[i] * (fr[i] - 1)* (fr[i] - 2)/2;
    }
    g << rez;
}