Project Euler 69

project_euler_69.rb

require 'prime'

class Integer
  def phi
    self.prime_division.inject(1){|m,(p,k)|m*=p**k-p**(k-1)}
  end
  def phi_ratio
    self.to_f / self.phi
  end
end

def project_euler_69 n_max=1_000_000
  (2..n_max).max_by(&:phi_ratio)
end

if $0 == __FILE__
  p project_euler_69
end