for n in (1 .. 2**19) {
    var frac = 0

    n.divisors.each {|d|
        frac += 1/d
    }

    if (frac.is_int) {
        say "Sum of reciprocal divisors of #{n} = #{frac} exactly #{
            frac == 2 ? '- perfect!' : ''
        }"
    }
}