Wikipedia for mathematicians 1: Why contribute?
edit- Wikipedia is growing (somewhat more slowly, recently): 4.000.000+ articles (as of December 2012), of which about 28.000 are on mathematics.
- The better the articles get, the more experienced and knowledgeable writers it needs to improve them. The number of editors is declining.
- Wikipedia articles are highly visible: google queries on scientific topics typically show Wikipedia first: stratification Sperner's lemma, Random graphs.
- Wikipedia writing is easy, fun, and also improves your writing skills.
- Everybody, including you, is using Wikipedia, so sharing your knowledge will make it even better.