#include<fstream.h>
int v[7001];
int main()
{
 int  x,s,i,j,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;
 }