#include <fstream>

using namespace std;

ifstream cin ( "medie.in" );
ofstream cout ( "medie.out" );

#define VMAX 7000

int f[VMAX + 1];

int main() {
    long long n, i, ans, x, j;
    cin >> n;
    for ( i = 0; i < n; i++ ) {
        cin >> x;
        f[x]++;
    }
    ans = 0;
    for ( i = 1; i <= VMAX; i++ ) {
        ans += f[i] * ( f[i] - 1 ) * ( f[i] - 2 ) / 2;
        if ( i < VMAX / 2 ) {
            for ( j = i - 1; j > 0 ; j-- ) {
                ans += f[j] * f[2 * i - j] * f[i];
            }
        }
        else {
            for ( j = i + 1; j <= VMAX; j++) {
                ans += f[j] * f[i] * f[2 * i - j] * f[i];
            }
        }
    }
    cout << ans;
    return 0;
}