42

The Ultimate Answer to the Ultimate Question of Life, the Universe and Everything.

But don't you dare go looking for the question. If you find it, the universe will be replaced with something even stranger. And that might not necessarily be a good thing. Of course, some say that this has already happened.

Also, 24 reversed. (The Doctor Who episode named "42" was a reference to this, since it took place in real time over 42 minutes.)

00101010 in binary. 52 in octal. 2A in hexadecimal. 10 in base 42.