#include<stdio.h>

int v[7001];

int main()
{int S=0,i,j,k,n,nr,x;

 FILE* f=fopen("medie.in", "r");
 FILE* g=fopen("medie.out","w");

 fscanf(f, "%d", &n);


 for(i=1;i<=n;i++)
    {fscanf(f, "%d", &x);
     v[x]++;
     }


 for(i=1;i<=n;i++)
   {nr=v[i];
    S=S+((nr-2)*(nr-1)*nr)/2;
    j=i-1; k=i+1;

    while(j>=1 && k<=n)
      {if(v[j] && v[k]) S+=(v[i]*v[j]*v[k]);
       j--;
       k++;
       }

    }


 fprintf(g, "%d", S);

 fclose(f);
 fclose(g);
    
 }