#include<stdio.h>
#define N 7001
int cate[N];
int main()
{
    FILE *fin,*fout;
    fin=fopen("medie.in","r");
    fout=fopen("medie.out","w");
    int n;
    fscanf(fin,"%d",&n);
    int i;
    for(i=0;i<n;i++)
    {
        int nr;
        fscanf(fin,"%d",&nr);
        cate[nr]++;
    }
    long long sol=0;
    for(i=0;i<N;i++)
    {
        sol+=((long long)(cate[i]-1)*cate[i]*(cate[i]-2))/2;
        int j;
        for(j=i+2;j<N;j+=2)
            sol+=(long long)cate[j]*cate[i]*cate[(i+j)/2];
    }
    fprintf(fout,"%lld\n",sol);
    return 0;
}