Have you noticed that whenever you get one of those 6 or 8 digit authenticator codes there's an easy mental way to chunk it? E.g. consecutive numbers, palindromes, repeats, familiar sequences (e.g. 911, 1066, etc). Presumably this is all just randomness, but could you make a least-memorizable code?
@zachweinersmith.bsky.social I read something once that your brain remembers about the same amount of numbers in the short term, regardless of how many digits are in it. So you can break apart numbers like that to remember them more easily. Like if your code was 982476, you could remember is as 98, 24, 76 and that's only three numbers to your brain.