#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, k;
    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;
        for ( j = i - 1, k = i + 1; j >= 1 && k <= VMAX; j--, k++ ) {
            ans += f[i] * f[j] * f[k];
        }
    }
    cout << ans;
    return 0;
}