#include <fstream.h>
int v[7001];
int main ()
{ int i,j,k,s,n,x;
ifstream f ("medie.in");
ofstream g ("medie.out");
f>>n;

for (i=1;i<=n;i++) {f>>x;v[x]++;}
s=0;
for (i=1;i<=7001;i++){
    k=v[i];
    s+=(k-1)*(k-2)*k/2;j=i-1; k=i+1;
    while (j>=1 && k<=7001) {
	      if (v[j]>0 && v[k]>0) s+=v[i]*v[j]*v[k];
		j--; k++; } }
g<<s;

f.close ();
g.close();
return 0;
}