A little late for Day 18 of #mathober I present my first #manim animation.
(The low quality version seems good enough, is it?)

Day 15 of #mathober is(?) "Irredundant".
Being irredundant is another property that a subset of the set of nodes of a graph can have.

Imagine we put a guard on some of the nodes of a graph, and each one protects the node they are on, and the neighboring nodes. (We don't insist that alltogether all the nodes are protected, that would need the guards to occupy a dominating set.)
If there is a guard that we can remove without decreasing the number of protected nodes, that guard is redundant. If there is no such guard, the set of nodes they occupy is irredundant.

The empty set is irredundant, the set of all nodes usually isn't (when is it?).

Consider the line graph with 7 nodes
0—1—2—3—4—5—6.
If Riley stands at 2 and Spike at 4, then all nodes except 0 and 6 are protected, and either one leaving would put a formerly protected place at risk, so {2,4} is irredundant.
If Buffy appears at 3, she may feel redundant, because {2,3,4} is not irredundant.

To compute the terms, I used one of my favorite tools: binary decision diagrams (BDDs).
BDDs are a way to represent boolean formulas, and if a formula can reasonably be represented by a BDD (one can get an intuition for when that is the case) you can count for how many inputs the formula is true much faster than you would otherwise expect.
In this case, we have one boolean variable for each field, indicating whether this field is occupied by a zebra. The formula expresses the condition that all field are occupied or attacked.

I had almost everything done previously, I only had to add a class defining the zebra graph.

While Day 2 of #mathober didn't inspire me to do art, it did inspire me to compute three more terms (6–8) of OEIS-A387437 (Number of dominating sets in the n X n zebra graph).

The zebra is a piece of fairy chess that moves similar to a knight, but instead of moving one step in one direction and two steps in an orthogonal direction, it moves two and three.
A zebra graph has the fields of a chess board as nodes, and its edges connect nodes/fields when a zebra can get from one to the other in one move.
A dominating set of a graph is a subset of the nodes such that each node of the graph is either in subset, or a neighbor of (i.e. connected via an edge to) a node in the subset.

So we are asked about the number of ways to put zebras on a board so that every field is occupied or attacked by a zebra.

A zebra can't move on a 3 X 3 (or smaller) board, so in this case the only way is to put a zebra on every field. That means that the first three terms of the sequence are 1 for a trivial reason.
…

Mense: "Ich halte es für falsch zu denken, diese Normalisierung wäre ein taktisches Mittel der Parteien der Mitte, um die Wählerschaft am rechten Rand abzuholen. Ich glaube eher, das zeugt davon, dass diese Einstellungen genuin aus dieser Mitte entstehen, die sich selbst immer weiter nach rechts bewegt."

Gutes Interview mit Thorsten Mense und Thomas Ebermann zu ihrem neuen Ding "Normal", auf das ich sehr gespannt bin.
https://taz.de/Comedy-Duo-ueber-deutschen-Irrsinn/!6063752/