Mathematics sites

General

• PlanetMath.org – http://planetmath.org/
• On-Line Encyclopedia of Integer Sequences – http://oeis.org/ | http://www.research.att.com/~njas/sequences/
• The Internet Encyclopedia of Science – http://www.daviddarling.info/encyclopedia/ETEmain.html
• Die Mathe-Redaktion – http://matheplanet.com/matheplanet/nuke/html/index.php [in German]
• EqWorld – The World of Mathematical Equations – http://eqworld.ipmnet.ru/index.htm
• MapleSoft’s Mathematics help database – http://www.maplesoft.com/support/help/category.aspx?cid=1887
• Wolfram MathWorld – http://mathworld.wolfram.com/

Matrices

• “The Matrix Cookbook”: http://matrixcookbook.com/
• The University of Florida Sparse Matrix Collection: http://www.cise.ufl.edu/research/sparse/matrices/

Online symbolic calculators

• Wolfram Integrator: http://integrals.wolfram.com/index.jsp | also see the Wolfram Alpha: http://www.wolframalpha.com/
• Mathematical Assistant on Web: http://user.mendelu.cz/marik/maw/index.php?lang=en
• Function calculator: http://wims.unice.fr/wims/wims.cgi?module=tool/analysis/function.en
• Integral Calculator: http://www.numberempire.com/integralcalculator.php
• Mathomatic Service on the Web – http://mathomatic.orgserve.de/CGI/math.php
  • Mathomatic: project page at FreshMeat – http://freshmeat.net/projects/mathomatic | Home – http://mathomatic.org/math/ | download – http://mathomatic.org/math/download.html

Geometry

• Polycell = Glossary of Hyperspace – http://web.archive.org/web/20070207021813/members.aol.com/Polycell/glossary.html:
  • Uniform Polytopes in Four Dimensions – http://web.archive.org/web/20070204075028/members.aol.com/Polycell/uniform.html

Topology

• Allen Hatcher’s pages – http://www.math.cornell.edu/~hatcher/.
  • Elements of his books: Topology of Numbers – http://www.math.cornell.edu/~hatcher/TN/TNpage.html | Algebraic Topology – http://www.math.cornell.edu/~hatcher/AT/ATpage.html | Vector Bundles & K-Theory – http://www.math.cornell.edu/~hatcher/VBKT/VBpage.html | Spectral Sequences in Algebraic Topology – http://www.math.cornell.edu/~hatcher/SSAT/SSATpage.html
  • Course notes: Notes on Basic 3-Manifold Topology – http://www.math.cornell.edu/~hatcher/3M/3Mdownloads.html | Notes on Introductory Point-Set Topology – http://www.math.cornell.edu/~hatcher/Top/Topdownloads.html
  • Books by other authors: Hans Samelson “Notes on Lie Algebras” (3rd edition; 1989) – http://www.math.cornell.edu/~hatcher/Other/Samelson-LieAlg.pdf | Heinz Hopf “Selected Chapters of Geometry” (write-up by Hans Samelson of lectures by Hopf’s 1940 lectures) – http://www.math.cornell.edu/~hatcher/Other/hopf-samelson.pdf

Differential Equations

• “Ordinary Differential Equations” at EqWorld (The World of Mathematical Equations) – http://eqworld.ipmnet.ru/en/solutions/ode.htm
• Differential Equations at MapleSoft – http://www.maplesoft.com/support/help/category.aspx?cid=1939 | Classification of ODEs – http://www.maplesoft.com/support/help/category.aspx?CID=1940

Books online

• “Elements of Abstract and Linear Algebra” by Edwin H. Connell – http://www.math.miami.edu/~ec/book/
• “Sean’s Applied Math Book” – http://www.its.caltech.edu/~sean/book.html
• “Digital Library of Science” by Florentin Smarandache – http://fs.gallup.unm.edu/eBooks-otherformats.htm
• Science & Engineering books for free download – http://www.techbooksforfree.com/science.shtml
• Related here at this blog: Books online – https://eikonal.wordpress.com/2010/01/04/books-online/ | Physics books online – https://eikonal.wordpress.com/2010/03/28/physics-books-online/