#include<fstream.h>
int v[7001];
int main ()
{int n, s=0, i, j, k, x;
ifstream f ("medie.in");
ofstream g ("medie.out");
f>>n;                
for (i=1; i<=7000; i++) v[i]=0;
for (i=1; i<=n; i++) {f>>x;
		      v[x]++;}
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;
}