I asked my local LLM to add 23 numbers and got seven wrong answers (viggy28.dev)

Have you thought of using a calculator for this task?

Though it’s obvious, nice write up. This is the kinda rabbit hole I enjoy going through and reading.

This kind of thing beats me. Why should a "Large Language Model" be expected to act as a calculator. Clue one is on the name, clue two might be an understanding that it is based on statistics, it is not the deterministic tool you need.