Finds the greatest prime factor of a number. Answer to http://projecteuler.net/problem=3

greatest_prime_factor.rb

def greatest_prime_factor(n)
  divider = 2
  finder = n
  factors = []
  while divider < finder
    if n%divider == 0
      factors << divider
      finder = finder/divider
      factors << finder
    end  
    if divider.even?
      divider = divider + 1
    else
      divider = divider + 2
    end


  end
  factors.sort {|x,y| y <=> x }.each do |factor|
    return factor unless is_not_prime? factor
  end


  
end

def is_not_prime?(n)
  divider = 2
  while divider < n
    return true if n%divider == 0
    divider = divider + 1
  end
  return false
end