17 is the one arbitrary random number. It's also called a "Feller" number. Feller, who was a Princeton man but is now dead, always used to say, "Pick any random number4, say 17." The point is, if you're going to pick an arbitrary number, you don't want it to be even, and you want it to be less than 20. 19 is pushing it a little. Also, it better not be divisible by 5 if it's going to be random. 1 is obviously out. 3 is the Trinity; that's no good. 5 is divisible by 5, so we don't want that. 7 is lucky; 9 is a perfect square. 11 is also lucky, as in "7 come 11." 13 is unlucky, and 15 is divisible by 5. We've already thrown out all the evens, so 17 is the only number that's left.
University, Winter 1970-71
Note: I know this quotation is strange...and that I may be the only one in the world who thinks it is interesting.