for n in (2..20, 65) {

    var steps = []
    var orig = n

    for (var f = n.factor; true; f = n.factor) {
        steps << f
        n = Num(f.join)
        break if n.is_prime
    }

    say ("HP(#{orig}) = ", steps.map { .join('_') }.join(' -> '))
}