project-euler/Sidef/021 Amicable numbers -- v2.sf

#!/usr/bin/ruby

# Daniel "Trizen" Șuteu
# https://github.com/trizen

# For example, the proper divisors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110; therefore d(220) = 284.
# The proper divisors of 284 are 1, 2, 4, 71 and 142; so d(284) = 220.
# Evaluate the sum of all the amicable numbers under 10000.

# https://projecteuler.net/problem=21

# Runtime: 0.393s

func proper_sigma(n) {
    n.sigma - n
}

var total = 0

for a in (2 ..^ 10000) {

    var b = proper_sigma(a)
    next if (b <= a)
    var c = proper_sigma(b)

    if (c == a) {
        say "#{a} #{b}"
        total += a+b
    }
}

say total