#include<stdio.h>
long long int n,i,j,a,c[7001],sol,st,dr,r,m;
int main()
{
	FILE *f,*g;
	f=fopen("medie.in","r");
	g=fopen("medie.out","w");
	fscanf(f,"%lld",&n);
	for(i=1;i<=n;i++)
	{fscanf(f,"%lld",&a);c[a]++;}
	for(i=1;i<=6998;i++)
	if(c[i])
	{ sol+=(c[i]*(c[i]-1)*(c[i]-2))/2;
	  st=i-1;dr=7000-i;
	  m=(st<dr)?st:dr;
	  for(r=1;r<=m;r++)
	  sol+=c[i-r]*c[i]*c[i+r];
	}
	fprintf(g,"%lld\n",sol);
	fcloseall();
	return 0;
}