I suspect everyone has a book they dip into from time to time, but never read cover-to-cover. My two are an anthology of Scottish folk stories, and The Penguin Dictionary of Curious and Interesting Numbers.
(I tried reading the dictionary straight through once but only got as far as 1.082323.)
That latter book might be about to be superseded though. How about The Encyclopaedia of Integer Sequences? Even better, it has an online companion.
I think I've found geek heaven. Those Scottish folk stories will have to wait a while.
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