Double-precision floating-point implementations of the gamma function and its logarithm are now available in most scientific computing software and special functions libraries, for example TK Solver, Matlab, GNU Octave, and the GNU Scientific Library.

https://en.m.wikipedia.org/wiki/Gamma_function

The program is named after Octave Levenspiel, a former professor of the principal author. Levenspiel was known for his ability to perform quick back-of-the-envelope calculations.[8]

https://en.m.wikipedia.org/wiki/GNU_Octave

In the natural sciences, back-of-the-envelope calculation is often associated with physicist Enrico Fermi,[2] who was well known for emphasizing ways that complex scientific equations could be approximated within an order of magnitude using simple calculations. He went on to develop a series of sample calculations, which are called "Fermi Questions" or "Back-of-the-Envelope Calculations" and used to solve Fermi problems.[3][4]

https://en.m.wikipedia.org/wiki/Back-of-the-envelope_calculation

The estimation technique is named after physicist Enrico Fermi as he was known for his ability to make good approximate calculations with little or no actual data. Fermi problems typically involve making justified guesses about quantities and their variance or lower and upper bounds. In some cases, order-of-magnitude estimates can also be derived using dimensional analysis.

https://en.m.wikipedia.org/wiki/Fermi_problem