#include <fstream>
using namespace std;
ifstream f ("medie.in");
ofstream g ("medie.out");
unsigned long long nr;
int n,i,j,v[7001],t,mare,st,dr;
int main()
{
    f>>n;
    for(i=1;i<=n;++i)
    {
        f>>t;
        ++v[t];
        if(t>mare) mare=t;
    }
    for(i=1;i<=mare;++i)
    {
        nr=nr+(v[i]-2)*(v[i]-1)/2*v[i];
        if(v[i])
        {
            st=i-1;
            dr=i+1;
            while(st>=1&&dr<=7000)
            {
                if(v[st]&&v[dr]) nr=nr+v[st]*v[dr]*v[i];
                ++dr;--st;
            }
        }
    }
    g<<nr;
    return 0;
}