The NR3 Dependencies Tool figures out exactly which .h files (and in which order) you need to include, based on routines that you are using.
Confused about which NR3 routines are in which .h files, or in which chapters, sections, or pages? Use the Dynamic Index of Routines tool.
You can call Numerical Recipes routines (along with any other C++ code) from Python. A tutorial with examples is here. A free interface file is here. These files are a bit out of date, so you might have to do some experimenting.
If you are interested in time-series, check out the Fast Statistical Methods Page. It contains links and public-domain code for some interesting techniques.
When you need mathematical software that can be freely redistributed as source code (which Numerical Recipes can't), a good place to look is Netlib. Within Netlib, the SLATEC package offers a comprehensive collection of (alas, Fortran only) source code.
Many Numerical Recipes readers are also interested in the Chemehuevi language ;)
Interested in Albrecht Dürer's magic square, as featured in the Dan Brown book?
Interested in the principles behind moving averages (a.k.a. sliding window averages)?
Interested in how Large Language Models like ChatGPT or GPT-4 actually work?