7:16 AM
Jan 27 at 6:42, by Martin Sleziak
[meta-tag:deleted-tag} The tags , and are gone.
It seems that I was actually wrong - there is still one question tagged .
2

Let $(p_i)$ be the sequence of prime numbers. Can we solve the equation: $$\sum_{i=1}^k p_i^2=\frac{n(n+1)}{2}$$ in $(k,n)$? Note that $(7,36)$ is solution. Is this the unique solution?

I have posted some SEDE querie here: chat.stackexchange.com/transcript/10243/2023/1/27
Looking at the removals it seems that there was a big clean-up in 2013.
The tag appeared a few times after that: January 2014, March 2014, August 2014, January 2023 - but in each case I only found a single question.
Looking at the Wayback Machine it seems that this was the tag-info: mathoverflow.net/posts/142965/revisions
But it only said: "Deprecated; please use a more specific tag." (Created by François G. Dorais in 2013.)

8 hours later…
3:29 PM
Sep 2 at 22:43, by Martin Sleziak
Now there are four questions tagged .
3

Definition 1. An affine plane is a pair $(X,\mathcal L)$ consisting of a set $X$ and a family $\mathcal L$ of subsets of $X$ called lines which satisfy the following axioms: Any distinct points $x,y\in X$ are contained in a unique line $L\in\mathcal L$; Any line $L\in \mathcal L$ contains at le...