#include <stdio.h>
#define nmax 9005


int N, i, A[nmax], V[nmax], v1, v2, ans, max;

void read()
{
	freopen("medie.in", "r", stdin);
	for (scanf("%d", &N), i = 1; i <= N; ++i)
		scanf("%d", A+i);
}

void write()
{
	freopen("medie.out", "w", stdout);
	printf("%d", ans);
}

void solve()
{
	for (i = 1; i <= N; ++i)
	{
		++V[A[i]];
		if (A[i] > max)
			max = A[i];
	}

	// pentru valori diferite
	for (v1 = 1; v1 <= max; ++v1)
		for (v2 = v1+2; v2 <= max; ++v2, ++v2)
			if (V[v1] && V[v2] && V[(v1+v2)>>1])
				ans += V[v1] * V[v2] * V[(v1+v2)>>1];

	// pentru aceeasi valoare
	for (v1 = 1; v1 <= max; ++v1)
		if (V[v1] >= 3)
			ans += V[v1] * (V[v1]-1) * (V[v1]-2) >> 1;
}

int main(void)
{
	read();

	solve();

	write();

	return 0;
}