#include<stdio.h>
int v[7001];
FILE *f=fopen("medie.in","r");
FILE *g=fopen("medie.out","w");

void citire(int v[7001],int &n)
{int x;
 fscanf(f,"%d",&n);
 for (int i=1;i<=n;i++) {fscanf (f,"%d",&x);
			 v[x]++;
			 }
}

int main()
{int i,j,k,n,nr,s=0;
 citire(v,n);
 for (i=1;i<=n;i++) {nr=v[i];
		     s+=((nr-1)*(nr-2)*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);
 return 0;
}