The prime factors of 13195 are 5, 7, 13 and 29.
What is the largest prime factor of the number 600851475143 ?
[code=ruby]n = 600851475143
pf = 1
2.upto(Math.sqrt(n).floor) do |d|
pf = d if n % d == 0
n /= d while n % d == 0
break if n == 1
end
puts pf[/code]
Nie wychodząc poza stdlib:
require 'prime'
600851475143.prime_division.max.first # => 6857