Ever wondered what comes next, and why? The On-Line Encyclopedia of Integer Sequences has the answers. (Previously.)
posted by parudox on Mar 10, 2009 - 33 comments

World of Science contains budding encyclopedias of astronomy, scientific biography, chemistry, and physics. This resource has been assembled over more than a decade by internet encyclopedist Eric Weisstein with assistance from the internet community. MeFi visited Weisstein's Mathworld a couple years ago.
posted by netbros on Feb 18, 2009 - 6 comments

Online Encyclopedia of Mathematics Edited by Michiel Hazewinkel (CWI, Amsterdam), and originaly published in dead tree form in 2002, now free to browse and poke into. [more inside]
posted by Iosephus on Aug 2, 2008 - 7 comments

More than fifty selected articles from The Princeton Companion of Mathematics (username: Guest, password: PCM) — a thematically-organized compendium of mathematics and mathematicians from Fields Medal-winner Tim Gowers. [via, previously]
posted by Blazecock Pileon on Sep 27, 2007 - 8 comments

Can you stump the Encyclopedia of Integer Sequences? Every identifiable sequence known to man, including:

Name: Busy Beaver problem: maximal number of steps that an n-state Turing machine can make on an initially blank tape before eventually halting.
Comment: The sequence grows faster than any computable function of n, and so is non-computable.
Keywords: hard,huge,nice,nonn,bref

If your sequence does not appear there, you might want to try the Super Seeker.
posted by vacapinta on Apr 15, 2002 - 9 comments