#include<stdio.h>

#define ll long long
#define maxim(a,b) (a>b ? a : b)

int f[7006],vm;
int v[9007],n;
ll sol;

int main ()
{
    int i,j,aux;
    freopen("medie.in","r",stdin);
    freopen("medie.out","w",stdout);
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        scanf("%d",&v[i]);
        f[v[i]]++;
        vm=maxim(vm,v[i]);
    }
    for(i=1;i<=vm;i++)
    {
        if(!f[vm])
            continue;
        f[i]--;
        for(j=i+1;j<=vm;j++)
        {
            if(!f[j] || ((i+j)&1))
                continue;
            f[j]--;
            aux=(f[j]+1)*(f[i]+1);
            sol+=(ll)f[(i+j)/2]*aux;
            f[j]++;
        }
        f[i]++;
    }
    for(i=1;i<=vm;i++)
        if(f[i]>2)
            sol+=(ll)f[i]*(f[i]-2)*(f[i]-1)/2;
    printf("%lld\n",sol);
    return 0;
}