TITLE: Mathematics, Philosophy and writing.
QUESTION [12 upvotes]: Do you know of any famous mathematicians who were also philosophers? I have heard of Descartes, Plato and Leibniz. Are there other good examples, especially more modern examples? 
Also welcome are works of literature which use mathematics in descriptions and use mathematical properties in their works (maybe like Borges in the Book of Sand, or Flatland by Edwin Abbott).

REPLY [2 votes]: Does not exactly fit the question, but:
Edmund Husserl, made his doctorate in math, worked as assistant of Weierstrass. Afterwards he devoted himself to philosophy, and became one of the most ininfluential philosophers of the XX century (and not in the "analytic" branch).
And perhaps even less pertinent, but interesting nevertheless:
André Weil, was certainly not a philosopher; but, besides having more humanistic formation and interests than most mathematicians, he had a sister who was a philosopher (in the wide sense): the great Simone Weil. She herself wrote some things about science and math, though that's not the best from her IMO.