prime_factor.rb

def next_prime(number)
	prime=false
	while prime==false
		number+=1
		for i in 2..number
			prime=true if i==number
			break if number % i ==0
		end
	end
	return number
end

def prime_factor(number)
	factors=Array.new
	prime=2
	while prime<=number
		if number % prime==0
			until number % prime != 0
				number=number/prime
				factors.push(prime)
			end
		end
		prime=next_prime(prime)
	end
	return factors.max
end

p prime_factor(600851475143)