#include<fstream.h>  
int v[7001];  
int main ()  
{int n, s=0, i, j, k, x;  
ifstream f ("medie.in");  
ofstream g ("medie.out");  
f>>n;                  
for (i=1; i<=7000; i++) v[i]=0;  
for (i=1; i<=n; i++) {f>>x;  
              v[x]++;}  
for (i=1; i<=7000; i++) {k=v[i];  
              s+=((k-2)*(k-1)*k)/2;  
              j=i-1;  
              k=i+1;  
              while (j>=1 && k<=7000) {if (v[j]>0 && v[k]>0) s+=v[i]*v[j]*v[k];  
                           j--;  
                           k++;  
                                               }  
              }  
g<<s;  
f.close();  
g.close();  
return 0;  
}