#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;   
}