The Carmichael λ function currently resides in the sage.crypto.util module, but it's really much more general than "just" crypto: λ(n) is the exponent of the unit group of ℤ/n. (The morally comparable Euler φ function does live in sage.arith.misc already.)

This patch lifts carmichael_lambda() out of obscurity, plus some tiny tweaks.

Component: algebra

Author: Lorenz Panny

Branch/Commit: 7e9aefc

Reviewer: Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/34719