gistfile1.rb

a=600851475143
#a=11351340
last_prime= 2
counter= 2
prime_factors= []
factoring= 1

def factor_by(number, factor)
  if number.modulo(factor) == 0
    @count= @count.nil? ? 1 : @count+1
    factor_by(number/factor, factor)
  end
  return @count;
end

if a.modulo(2) == 0
  prime_factors=[2]
  @count= nil
  factoring= factoring*(2**factor_by(a,2))
  counter= 3
end


while(factoring != a) do
  next_me= false
  if a.modulo(counter) == 0
    prime_factors.each do |p| 
      if counter.modulo(p) == 0
        counter= counter+1
        next_me=true 
      end
    end
    next if next_me
    @count= nil
    factoring= factoring*(counter**factor_by(a,counter))
    last_prime = counter
    prime_factors << last_prime 
  end
  counter= counter+1
end

p prime_factors