I am glad they did this to you at no extra charge. But then, isn't 666 the devil's number?
It's the "Number of the beast" I'd be happy if I got three sixes. Cool info on its mathematical properties
can be found here
Other, more amusing, facts about the beast
are here.
I find this kind of thing just as silly/amusing as not having floor 13 in hotels. Still, it's nice that NW changed things to make you feel better.