#include <cstdio>

using namespace std;
long long f[7001];
int main()
{
    FILE *fin=fopen ("medie.in","r");
    FILE *fout=fopen ("medie.out","w");
    int n,i,x,nc,nmic,nmare,j;
    long long sol;
    fscanf (fin,"%d",&n);
    for (i=1;i<=n;i++){
        fscanf (fin,"%d",&x);
        f[x]++;
    }
    sol=0;
    for (i=1;i<=7000;i++){
        nc=i;
        if (f[nc]>=3)
            sol=sol+(f[nc]*(f[nc]-1)*(f[nc]-2))/2;
        for (j=1;j<=7000;j++){
            nmic=i-j;
            nmare=i+j;
            if (nmic>0 && nmare<=7000 && f[nmic] && f[nmare])
                sol=sol+f[nmic]*f[nc]*f[nmare];
        }
    }
    fprintf (fout,"%lld",sol);
    return 0;
}