#include<stdio.h>
int v[9001];
int main()
{int x,n,i,S=0,nr,k,j;

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<=7001;i++)
   {nr=v[i];
    S=S+(nr*(nr-1)*(nr-2)/2);
    j=i-1;
    k=i+1;
    while(j>=1 && k<=n) {if(v[j]!=0 && v[k]!=0) S=S+v[i]*v[j]*v[k];
                         j--;
			 k++;}
    }

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

fclose(f);
fclose(g);
return 0;
}