#include <fstream>
using namespace std;
ifstream f("medie.in");
ofstream g("medie.out");
long long n, rez, mx, v[9005], ap[7005];

int main()
{
    f>>n;
    for (int i=1; i<=n; i++)
    {
        f>>v[i];
        mx = max(mx, v[i]);
        ++ap[v[i]];
    }
    for (long long i=1; i<=mx; i++)
    {
        rez+=(ap[i]-1)*(ap[i]-2)/2*ap[i];
        for (long long j=i+1; j<=mx; j++)
            if(ap[i]>0 && ap[j]>0 && (i+j)%2==0)
                rez+=ap[(i + j)/2]*ap[i]*ap[j];
    }
    g<<rez;
    return 0;
}