Bronshtein, Semendyayev, Musiol, Mühlig: Handbook of Mathematics, 6th Edition

• https://en.wikipedia.org/wiki/Special:BookSources/978-3662462201
• https://de.wikipedia.org/wiki/Spezial:ISBN-Suche/978-3662462201
• http://www.amazon.de/dp/3662462206
• https://de.wikipedia.org/wiki/Taschenbuch_der_Mathematik – nowadays (resp. for quite some while) there have been 2 parallel editions (plus translations) of this classic math book

As of 2015-04-02 you can’t even purchase the 6th edition as paperback – but there are sources, where you get it as PDF. Isn’t that appalling?