#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 + 2; j <= maxc; j+=2)
                if(fr[j] && 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;
return 0;
}