Ask ChatGPT or any other LLMs to give you ten random numbers between 0 an 9, and it will give you each number once (most of the time). At most, one of the digits may appear twice in my experience.
Actually, when I just verified it, I got these:
Prompt: "Give me ten random numbers between 0 and 9."
> 3, 7, 1, 9, 0, 4, 6, 2, 8, 5 (ChatGPT, 5.3 Instant)
> 3, 7, 1, 8, 4, 0, 6, 2, 9, 5 (Claude - Opus 4.6, Extended Thinking)
These look really random.
Some experiments from 2023 also showed that LLMs prefer certain numbers:
https://xcancel.com/RaphaelWimmer/status/1680290408541179906