RIP Richard K. Guy https://aperiodical.com/2020/03/richard-k-guy-1916-2020/

Example 5 has long been a favorite of mine. So easy to investigate, so geometrical, and there is a pattern, just not the obvious one.

That goes from sort of understandable to completely cryptic in about 3 pages

> It will be proved by intimidation

Sounds like it worked!

Heh. You mean sort of understandable for part of the first sentence, ending with '35 examples of patterns." After that, no.

TLDR: You can't tell by looking (if your rule holds for all or only a small set of numbers).

You will need a maths degree for actually telling.

"Capricious coincidences cause careless conjectures."