How about November?
I know because my second grade teacher taught me a trick, a trick that I still use all these years later.
Ball your hands into fists.
Now look at them. Do you see how your knuckles make bumps and valleys?
If you assign each bump and valley a month of the year, in order, the bump-months will be the ones with 31 days, while the valleys will be the ones that only have 30 (except for February, which has 28-ish days).
Maybe a visual will help.
I’ve asked Newt to be my hand model:
I’ve always been amazed that this works so well.
And it’s not just that every other month has 31 days.
If you look at July and August, they are both on bumps and they both have 31 days.