183 Maximum product of parts.sf

#!/usr/bin/ruby

# Daniel "Trizen" Șuteu
# Date: 18 October 2017
# https://github.com/trizen

# https://projecteuler.net/problem=183

# Runtime: 0.550s

define e = Num.e

say sum_by(5..10_000, {|n|
    var M = round(n/e)
    var r = M/gcd(n, M)

    r.remdiv!(2)
    r.remdiv!(5)

    r == 1 ? -n : n
})