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Randall Munroe's book "xkcd, volume 0" uses a rather odd number system for the page numbers. The first few page numbers are
1, 2, 10, 11, 12, 20, 100, 101, 102, 110, 111, 112, 120, 200, 1000, 1001, ...
This looks a bit like ternary, but notice that he skips from 20 straight to 100, from 120 to...