## Post without words #21

Associate Professor of Computer Science at Hendrix College. Functional programmer, mathematician, teacher, pianist, follower of Jesus.
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### 17 Responses to Post without words #21

1. David Eppstein says:

OEIS knows the answer…

• Brent says:

Yes, and there’s an interesting story behind that entry — more later!

• Ajm says:

I looked up the OEIS sequence. The relationship to sums of non-negative integers is fascinating!

• Ajm says:

And I just realized why its true.

2. kaligule says:

Walking along the paths counterclockwise there is an constant number of right turns in each group of diagrams, increasing from group to group.

• Brent says:

Indeed! What about the total number of turns, both right & left?

• Ajm says:

The number of edges increases by 2 each group.

• Brent says:

That’s right. Now, how do these two observations relate?

• kaligule says:

To do a full turn I have to do 4 right turns, plus an equal number of additional left and right turns (assuming we don’t want loops.). So the number of right turns determines the number of left turns.

3. Denis says:

Took me a couple of looks but since the area and perimeter weren’t constant, there was a clear metric to check next. This would be an interesting challenge to automate, with removal of reflections and rotations and length variations and collision avoidance.

• Brent says:

“This would be an interesting challenge to automate” — that’s a very perceptive comment. In fact, the image you see above *was* generated in an automated way, and indeed, it was quite interesting! In a sense, I have been trying (off and on) to figure out how to generate this image for more than a year. I’ll explain more in future posts.

• Denis says:

Can’t wait! 🙂

• Ajm says:

Consider a regular 2n+2 gon with n-1 painted edges where n=1,2,3,4….
.
The various such painted polygons are represented by your shapes.

4. Naren Sundar says:

It’s just a very difficult game of Tetris 🙂

5. Ajm says:

Start with a square. We bite off one of the corners to get an L shape (see second image). We can aslo bite into an edge to get a C shape (see third image). The corner biting is worth 1 bite and the edge biting is worth 2 bites. For any right angled polygon, edge biting and corner biting is defined the same way. Your shapes are the sets of n-bitten squares where n=0,1,2,3,4.