There are three known errata as of 2-20-2026.
* In the second half of the proof of Proposition 3.7.1, the various primes
of x, y, z, a got a little convoluted. It's a good exercise to fix it.  
Thanks to Brenda Johnson of Union College for pointing this out.
* In Historical Remark 12.1.7, there is now yet another Mersenne prime!
It has well over forty million digits.  See the GIMPS press release
at https://www.mersenne.org/primes/?press=M136279841
* At the beginning of section 8.2 "Powers", it says the powers of a=2 begin
with 0, 2, 4, 1, but then immediately say 2^0=1.  Of course, the powers begin
with 1, 2, 4, 1.