#include <iostream>
#include <fstream>
#define NMax 9002
using namespace std;
ifstream f("medie.in");
ofstream g("medie.out");
int n,v[NMax],h[NMax];
int main ()
{
    int i,j,ct=0,max=0;
    f>>n;
    for (i=1;i<=n;i++)
    {
        f>>v[i];
        h[v[i]]++;
        if (max<v[i]) max=v[i];
    }
    n=max;
    h[n+1]=h[n+2]=0;
    for (i=1;i<=n;i++)
    {
        if (h[i])
            for (j=i+2;j<=n;j=j+2)
                if (h[j] && h[(i+j)/2])
                    ct=ct+h[i]*h[j]*h[(i+j)/2];
        if (h[i]>=3) ct=ct+h[i]*(h[i]-1)*(h[i]-2)/2;
    }
    g<<ct;
}