pairs.rb

#! /usr/bin/env ruby
# -*- coding: utf-8 -*-

class Integer
  def factors
    fail if self <= 0

    (1...self).select { |num| (self % num).zero? }
  end

  def sum_of_factors
    factors.reduce(0, :+)
  end

  def amicable_pair
    s = sum_of_factors
    if self < s && s.sum_of_factors == self
      return [self, s]
    else
      return nil
    end
  end
end

n = 1
loop do
  pair = n.amicable_pair

  puts "#{pair.first} #{pair[1]}" if pair

  n += 1
end