#include <bits/stdc++.h>
using namespace std;

fstream in ( "medie.in" , ios::in  );
fstream out( "medie.out", ios::out );

const int DIM = 7e3 + 5;

int frq[DIM];

int main( void ) {
    ios::sync_with_stdio( false );
    
    int n;
    in >> n;
    
    for( int i = 1; i <= n; i ++ ) {
        int x;
        in >> x;
        
        frq[x] ++;
    }
    
    long long ans = 0;
    for( int i = 1; i < DIM; i ++ ) {
        ans += 1LL * frq[i] * ( frq[i] - 1 ) * ( frq[i] - 2 ) / 2;
        
        for( int j = i + 2; j < DIM; j += 2 )
            ans += 1LL * frq[i] * frq[j] * frq[(i + j) / 2];
    }
    
    out << ans << endl;
    return 0;
}