#include <fstream>
using namespace std;
int n,fr[7001],x;
long long S;
ifstream f ("medie.in");
ofstream g ("medie.out");
int main()
{
    f>>n;
    for(int i=1;i<=n;i++)
    {
        f>>x;
        fr[x]++;
    }
    for(int i=1;i<=7000;i++)
        if(fr[i])
        {
            if(fr[i]>=3)
                S+=fr[i]*(fr[i]-1)*(fr[i]-2)/2;
            for(int j=i+2;j<=7000;j+=2)
                S+=fr[i]*fr[j]*fr[(i+j)/2];
        }
    g<<S;
    f.close();
    g.close();
    return 0;
}