What does a tattoo of the number 21 symbolize?

The number 21 can symbolize a lot of things, it has a lot of different backgrounds but to me the most interesting and important thing about 21 (which is why I've gotten a tattoo of it) is 21 grams is the weight of the soul.

I also love that if you double 21 you get the answer to the universe (Hitchhiker's Guide to the Galaxy).