Not only older issues of the Numerical Recipes books, but also classics such as
Handbook Abramowitz and Stegun, Handbook of Mathematical Functions (10th corrected printing, 1972)

Bateman, Erdelyi et al. (Bateman Manuscript Project)
Higher Transcendental Functions (vols. 1, 2, and 3)

and
Encyclopaedia Britannica the great 11th Edition (1911)

Found via https://www.hpmuseum.org/forum/thread-16251-post-142741.html#pid142741

Examples from the  LaTeX Cookbook https://www.packtpub.com/product/latex-cookbook/9781784395148

The Theoretical Physics Reference is an attempt to derive all theoretical physics equations (that are ever needed for applications) from the general and special relativity and the standard model of particle physics.

The goals are:

   All calculations are very explicit, with no intermediate steps left out.
   Start from the most general (and correct) physical theories (general relativity or standard model) and derive the specialized equations from them (e.g. the Schrödinger equation).
   Math is developed in the math section (not in the physics section).
   Theory should be presented as short and as explicitly as possible. Then there should be arbitrary number of examples, to show how the theory is used.
   There should be just one notation used throughout the book.
   It should serve as a reference to any physics equation (exact derivation where it comes from) and the reader should be able to understand how things work from this book, and be ready to understand specialized literature.

Collection of short interviews with 14 Lisp programmers.

The second edition of the book Structure and Interpretation of
Computer Programs (SICP) in info format. The HTML version can be found on https://mitpress.mit.edu/sites/default/files/sicp/index.html

Links and recommendations for books about astronomical algorithms.

The links from this page display HTML renderings of the man pages from the Linux man-pages project as well as a curated collection of pages from various other free software projects.
From the author of
The Linux Programming Interface
http://man7.org/tlpi/index.html

Sounds like an interesting book. The blog is worth reading as well.

Search engine for books.

This is an all new two volume text, completely revised Jan 2011,
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