My kid is playing Pokemon Let's Go Pikachu, and he named his Pikachu "muchop", along side the actual machop in his party.

I always knew he had chaotic alignment

There are some more in a similar spirit, A053873 and A053169: oeis.org/wiki/Index_t...

This is the start of my "Depths of OEIS" series, btw

so the definition of this term should be changed." Neil Sloane replied the same day: "I disagree with the previous comment! I prefer the present, deliberately paradoxical, definition." In the age-old battle between whimsy and well-definedness, whimsy wins again.

There is an argument in the comments section, which starts with an unattributed "What is a(102288)?!" M. F. Hasler complained in 2017: "The term a(102288) has no possible value according to the present definition,

but I'm using A102288 because it has juicier comments) Even if there was a default value for the 102288-th entry in this sequence, it would contradict its own definition.

The second quirk is that A051070 leaves open the question of what the value of a(51070) is. It gets worse with A102288 (https://oeis.org/A102288 which is defined as 1 + the n-th term in sequence A`_`n. (There are some slight differences about offsets here,

and didn't already know about these OEIS entries, please let me know. I need this to be a common organic experience.

I could only find a short note in this Numberphile video (https://www.youtube.com/watch?v=ydn7s9-3GRc where Neil Sloane (who created OEIS and added these entries) mentioned that they're commonly used on math quizzes and tests. If you know someone who has used train lines on their quizzes,

this chips away even further at the idea that OEIS sequences need to have a mathematical definition removed from worldly messiness. Digging around,

the OEIS has roughly a dozen sequences of numbered stops on train lines. A000053 is "Local stops on New York City 1 Train (Broadway-7 Avenue Local) subway." A001049 is "Numbered stops in Manhattan on the Lexington Avenue subway." Of course,

The first is that the first time a(n) = -1 occurs, it's for n = 53 and 54, quoting the OEIS, "in both cases because the relevant New York subway lines do not have enough stops." What? Why are New York Subway lines involved? Turns out,

because A000066 (Smallest number of vertices in trivalent graph with girth (shortest cycle) = n) is only known up to 12 vertices. And then we get to my two favorite quirks about this sequence.

Not the fun ones, apparently. In the comments, Pontus von Brömssen noted that a(58) has 58669977298272603 digits, so it's too large to include in the database entry for A051070. a(66) is the first unknown value,

At first you might think, "what in the Gödel?" What if the arbitrary indexing of the OEIS changes over time? Aren't these sequences supposed to be defined by mathematical rules?

So the first term in A051070 is 1 because A000001 is the number of groups of order n, and that sequence has 1 as its entry in index 1. A000002 is the Kolakoski sequence (what? For another time) and has value 2 in entry 2. The sequence continues: 1, 2, 1, 0, 2, 3, 0, 7, 8, 4, 63, 1, 316, ...

A051070 (https://oeis.org/A051070 is a sequence about OEIS sequences. a(n) is the n-th term in sequence A`_`n (or -1 if A`_`n doesn't have enough terms).

Archived at: https://www.jeremykun.com/shortform/2026-04-09-0556/

This is so, so well-articulated.

First time seeing pentagonal magna tiles

Deterministic Primality Testing for Limited Bit Width

www.jeremykun.com/2026/04/07/deterministic...

Anthropic: we take security v seriously
Also Anthropic: our company culture is to ask the LLM to pretty please don't create vulnerabilities and then YOLO-ship unreviewed code.

Honestly, the great crisis of our society is the unwillingness of institutions to inflict consequences.

Impeach the president, fire the sex pests, expel cheating students, excommunicate an unrepentant heretic, prosecute the war criminals.

Believe in your institution enough to enforce its rules.

I think there's a lot more going on socially and psychologically than just "make money." They valorize risk and disruption and 100x payoffs. They don't want money, they want to be Zuck.

They're justifying their investment in AI companies. They tell every new batch of Y Combinator startups that they will fail if they're not positioning LLMs at the center of their business idea. They have been doing this for at least three years.

It's the same play as blockchain

Algebra works in mysterious ways

The Irrational Decision—A Book Review

www.jeremykun.com/2026/04/01/irrational-de...

To ace exams, get better at the easy questions Most tests are tests of speed, not tests of knowledge. Improve your speed to improve your results!

Tomorrow is the fifth annual April Cools! Let's celebrate with my favorite posts from the last few years:

2022: To Ace Exams, Get Better At The Easy Questions (predr.ag/blog/to-ace-...) by Predrag Gruevsky, with apparently an invalid handle. I've shared this post with others; it's real helpful!

If it were a big company I would bill the combined time of my involvement and the LLM working time (but not the time it's sitting idle before I have a chance to look at it)

Though it is probably a much harder question when it's your bottom line and reputation at stake.

A few days late, but indeed this one was really good. I even ordered Jill's book.

My contribution this year: a book review of Ben Recht's, "The Irrational Decision"

www.jeremykun.com/2026/04/01/i...