I vaguely remember another novel where a character gradually comes to realize that he's God. At one point he makes π be a rational number (there's a comment to the effect that it's sort of a relief for God to stop having to come up with more and more digits) and scientists and/or mathematicians are able to figure out that that's happened somehow -- maybe computers calculating π suddenly started coming up with this different number? (I think it would have been neat if e^πi suddenly stopped equaling -1 or something).

At the end of the book the Universe is destroyed and God creates a new one where planets follow square orbits.

Does this ring a bell for anyone?