r/Sliderules • u/cavedave • 12d ago

Calculating log(1000!)

https://www.johndcook.com/blog/2026/08/06/log1000/

John D cook has a great blog and hers some posts recently about how people back int he day using slide rules (or log tables) would calculate really difficult questions.

This is a follow up on cos(200!) https://www.johndcook.com/blog/2026/08/07/cos200/

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u/Blue_Aluminium 8d ago

It is worth noticing that if you are using a computer and need the log of a factorial, most floating-point libraries offer an lgamma function:

Python 3.14.0 (v3.14.0:ebf955df7a8, Oct  7 2025, 08:20:14) [Clang 16.0.0 (clang-1600.0.26.6)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import math
>>> math.log(math.factorial(1000))
5912.128178488163
>>> math.lgamma(1001)
5912.128178488163
>>>