#include<fstream>
using namespace std;
ifstream fi("medie.in");
ofstream fo("medie.out");
int fr[7001],s,i,j,k,n,x;
int main()
{
fi>>n;
for(i=1;i<=n;i++){fi>>x;fr[x]++;}
for(i=1;i<=7000;i++)
    {s+=(fr[i]-2)*(fr[i]-1)*fr[i]/2;
     for(j=i-1,k=i+1; j>=1&&k<=7000; j--,k++)
                        s+=fr[i]*fr[j]*fr[k];
    }
fo<<s;
return 0;
}