/// Macro para deducir la permutaci¢n.

/// Obtiene el \c i-‚simo d¡gito del n£mero \c n.
unsigned Formula2(unsigned n, unsigned i) {
    unsigned mult = 1;
    for (unsigned k=1; k<i; ++k) {
        mult *= 10;
    }

    return ( ( (n/mult) * mult) / mult ) % 10;
}