#include <stdio.h>

#define maxx 7010
#define ll long long

int n,m;
int c[maxx];
ll sol;

int main()
{
	freopen("medie.in","r",stdin);
	freopen("medie.out","w",stdout);

	int i,j,x;

	scanf("%d ",&n);

	for (i=1;i<=n;i++)
	{
		scanf("%d ",&x);
		c[x]++;
	}

	for (i=1;i<maxx;i++)
		for (j=i+2;j<maxx;j+=2)
			sol+=1LL*c[i]*c[j]*c[(i+j)/2];

	for (i=1;i<maxx;i++)
		sol+=c[i]*(c[i]-1)*(c[i]-2)/2;

	printf("%lld\n",sol);

	return 0;
}