gistfile1.rb

class Fixnum
  def factors
    (1..self).select { |f| modulo(f) == 0 }.uniq
  end

  def prime?
    equal? 1 or factors == [1, self]
  end

  def coprime?(b)
    hcf(b) == 1
  end

  def hcf(other)
    one = self
    while (one > 0 and other > 0) do
      one, other = [one, other].sort
      other %= one
    end
    return [one, other].max
  end
end