what's 54 in base 13?

That one elicits a bemused smile from Douglas Adams. I saw a BBC interview with him a couple of months ago where the "six-by-nine" thing was discussed, and he seemed to find it amusing that some readers took his work so seriously that they came up with that answer. In his words, "42 just seemed like a nice number, the sort of number you would happy to take home to meet your mother."