欧拉计划第三题

class 
  def max_prime(num)
    a = 2
    while a < num
      if num%a ==0
        num /= a
      else
        a +=1
      end
    end
    puts "the largest prime factor is #{num} "
  end
end
el = Euler_3rd.new
el.max_prime(600851475143)

the largest prime factor is 6857