I've had this puzzle on my phone for years. Every few months I'd glance at it and try and solve it. Last night, as I was eating dinner, I finally figured out the answer!

https://sh.itjust.works/post/55641581

Hah, took me nearly a minute.

Tap for spoiler

Add the digits on both sides. ? = 12

But I only got it so quickly because I enjoyed a similar puzzle once.

1
11
21
1211
111221
312211

continue the series.

312211

13112221
1113213211
31131211131221

Wonder if/when a 4 would ever show up… and what the formula for that would look like

Your mother’s a 4.
And your father smelt of elderberries! Harumphh

Yeah. Probably.

You realize a 4 never will happen, right?

Not with that attitude, it won’t

Edit: I found the nerdy stuff I was curious about

Edit edit: and the real good stuff

A005150 - OEIS