#include <fstream>
using namespace std;
ifstream cin("medie.in");
ofstream cout("medie.out");
long long f[7005];
int main()
{
    long long n,x,maxx=0,rasp=0;
    cin>>n;
    for(long long i=1;i<=n;++i)
    {
        cin>>x;
        f[x]++;
        if(x>maxx)
            maxx=x;
    }
    for(long long i=1;i<=maxx;++i)
    for(long long j=i;j<=maxx;j+=2)
    if(f[i]!=0 and f[j]!=0 and f[(i+j)/2]!=0)
    {
        if(i==j)
            rasp+=(f[i]*(f[i]-1)*(f[i]-2))/2;
        else rasp+=f[i]*f[j]*f[(i+j)/2];
    }
    cout<<rasp;
    return 0;
}