[dickfickling]

I have long considered building a code generator that only serves "nice" codes.

The standard implementation would use a hard coded set of patterns. The enhanced version would pair automatic random code generation with a public site where members of the public can decide in real time whether a given code is "nice" before it's sent along to the intended recipient.

(note @tptacek if you're reading this, I swear it's (mostly) a joke)

[cozzyd]

Hmm for 2 digits you only have one "nice" code (69). For three digits it's the same (069). For four digits you do get two (0069 and 6969), but I think you need a lot of digits before "nice" codes are effective.

[whalesalad]

I've always been under the impression that popular TOTP implementations were specifically designed to produce "nice" codes. They always have repeated digits, like 202838.

[wavemode]

I think that's just the birthday paradox. It's highly likely for a randomly generated number to have some repeated digits.