#include <stdio.h>

#define FOR(i,s,d) for(i=(s);i<(d);++i)
#define nmax 8192

int n,V[nmax],sol;

int main()
{
	freopen("medie.in","r",stdin);
	freopen("medie.out","w",stdout);
	int i,j,x;
	scanf("%d",&n);
	FOR(i,0,n)
	{
		scanf("%d",&x);
		V[x]++;
	}
	FOR(i,0,nmax)
	{
		sol+=V[i]*(V[i]-1)*(V[i]-2)/2;
		FOR(j,i+1,nmax)
		{
			x=(j<<1)-i;
			if(x>=nmax)
				break;
			sol+=V[i]*V[j]*V[x];
		}			
	}
	printf("%d\n",sol);
	return 0;
}