#include <cstdio>

using namespace std;
const int NMax = 8192;

int frec[NMax], cnt, N;

int main () {
	freopen ("medie.in", "r", stdin);
	freopen ("medie.out", "w", stdout);
	
	scanf ("%d\n", &N);
	
	int k;
	for (int i = 0; i < N; ++i) {
		scanf ("%d\n", &k);
		++frec[k];
	}
	
	for (int i = 0; i < NMax; ++i) {
		cnt += frec[i] * (frec[i] - 1) * (frec[i] - 2) / 2;
		for (int j = i + 1; j < NMax; ++j) {
			k = (j<<1) - i;
			if (k>=NMax) {
				break;
			}
		}
	}
	
	printf ("%d\n", cnt);
	
	return 0;
}