#include <stdio.h>
#define NMAX 7001
int N,a[NMAX];
long long sol;
int main(){
    int i,j,x;
    long long w;
    freopen("medie.in","r",stdin);
    freopen("medie.out","w",stdout);
    for (scanf("%d",&N);N;N--){
        scanf("%d",&x);
        ++a[x];}
    for (i=1;i<NMAX;++i){
      w=a[i];
      sol+=w*(w-1)*(w-2)/2;
      }
    for (i=1;i<NMAX;++i)
     for (j=i+1;j<NMAX;++j)
      if ((i+j)%2==0){
        x=(i+j)/2;
        sol+=(long long)a[i]*a[j]*a[x];
        }
    printf("%lld",sol);
    return 0;
}