#include <cstdio>
#include <cstdlib>
using namespace std;

int Freq[7010], N, ans, i, j, X;

int main()
{
    freopen("medie.in", "r", stdin);
    freopen("medie.out", "w", stdout);
    scanf("%i", &N);
    for(i = 1; i <= N; i++)
    {
        scanf("%i", &X);
        Freq[X] ++;
    }
    for(i = 1; i <= 7000; i++)
    {
        if(Freq[i])
            for(j = i + 2; j <= 7000; j += 2)
                if(Freq[j] && Freq[(i + j) / 2])
                    ans += Freq[i] * Freq[j] * Freq[(i + j) / 2];
        if(Freq[i] >= 3) ans += Freq[i] * (Freq[i] - 1) * (Freq[i] - 2) / 2;
    }
    printf("%i\n", ans);
    return 0;
}