#include <iostream>
#include <fstream>
#define Max 7000
using namespace std;
ifstream fin("medie.in");
ofstream fout("medie.out");
int j,i,ma,N,ap[7005],x;
long long cont;
int main()
{
    fin>>N;
    for(i=1;i<=N;i++)
    {
        fin>>x;
        ap[x]++;
    }
    for(i=1;i<Max;i++)
    {
        for(j=i+2;j<=Max;j++)
        {
            cont+=ap[i]*ap[j]*ap[(i+j)/2];
        }
        cont+=ap[i]*(ap[i]-1)*(ap[i]-2)/2;
    }
    fout<<cont<<"\n";
    return 0;
}