#include <fstream.h>
int v[7001];
int main()
{ int i,j,S,x,k,n;
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<=7000; i++) { k=v[i];
			  S+=(k-2)*(k-1)*k/2;
			  j=i-1;
			  k=i+1;
			  while (j>=1 && k<=7000){ if (v[j]>0 && v[k]>0)  S+=v[i]*v[j]*v[k];
						   j--;
						   k++;
						   }
		       }
g<<S;
f.close();
g.close();
return 0;
}