#include<fstream.h>  
int v[7001];     
int main()     
{int s,i,j,k,n,x;     
ifstream f("medie.in");     
ofstream g("medie.out");     
f>>n;     
s=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;     
 }