A triangular array of numbers. The bottom row is the counting numbers starting from 1. Each entry in the rows above that is the sum of the two entries below it. There is a joined "wave" curve starting from 1, going diagonally up and then down, first one step, then two steps, and so on - the waves get one step bigger each time.

Pin plot and logarithmic scatterplot of the sequence. The pin plot looks like several increasingly tall pointy towers. The logarithmic scatterplot is a rising and widening oscillating curve.

There's a very nice new sequence in the #OEIS: https://oeis.org/A387365

Such nice plots!

A117030 - OEIS

Competition time:

A sequence stats 1, k, ...

Each new term is the product of the last two subtract the sum of the other previous terms.

Which sequence grows faster k=1 or k=2 ?

#oeis

oeis.org/A117030

Editing history for sequence A307517. #8: I didn't get the signing code right. #9: go the signing code right. #10: removed the first 'prime' in "these are the nubmers whose largest prime divisor is not a prime power." #11: edits proposed. Discussion by Michel Marcus: "rather? largest proper divisor". Christian Perfect: "Yes, sorry! As you can see, I've had a bit of a brain muddle writing this simple comment." #12: add the word 'proper'. #12: edits proposed.

It's a one-line #OEIS comment, Michael, how many edits could it take? 10?

Original post on mathstodon.xyz

New in the #OEIS: the "it's my party and I'll cry if I want to" sequence: unhappy numbers sandwiched between two happy numbers.
https://oeis.org/A392990

A number is happy if the operation of squaring all its digits and summing the squares eventually leads to 1.

e.g.
68 → 100 → 1.
69 → 117 → 51 […]

A385673 - OEIS

103638 is an interesting number: when written in decimal, 103638! contains the substring 0123456789. No smaller factorial does.

From new #OEIS sequence https://oeis.org/A385673

A392387 - OEIS

#OEIS sequence that sounds like a Star Trek plot point: "Nullspace dimension of the periodic XX Heisenberg chain with n > 1 sites."
https://oeis.org/A392387

A392242 - OEIS

9814072356 is an interesting number: it's the largest square number (99066²) with no repeated digits.

From https://oeis.org/A392242 just added to the #OEIS.

A389543 - OEIS

New sequence just dropped to the #oeis

Start with the numbers [2,2,...] Then each new number is the product of the last two, written in mod n. The sequence stops when there is a repeating pair of consecutive numbers.

a(n) is the length of the above sequence.

oeis.org/A389543

#mathsky

A391013 - OEIS

New sequence just dropped to the #OEIS
Have you ever wondered how many sides are needed on a k-gon such that an inscribed and circumscribed k-gon calculates the area of a unit circle with accuracy bounds up to n digits? I know I have!
If you have a 12-gon will tell you π=3
oeis.org/A391013
#mathsky

Original post on mathstodon.xyz

5702631489 is an interesting number: 5702631489⁴ = 10575 50783 69274 13892 95697 10824 23634 08641.

It's the smallest number 𝑛 such that the decimal digits of 𝑛⁴ make up four copies of the digits of 𝑛.

And did you notice that 5702631489 uses every decimal digit?

Spotted in the new #OEIS […]

A390783 - OEIS

My new #OEIS sequence just dropped.

Least k > a(n-1) such that k + the sum of all previous terms = 0 (mod (k-2)), with a(1)=1 and a(2)=2.

1,2,3,4,...

(1+2+3+4+n) Is a multiple of (n-2).

...5,...

What comes next?

oeis.org/A390783

#mathsky

Original post on podcasts.social

Wisst ihr ohne Nachschauen, was die erste Folge in #OEIS ist?

Man würde ja denken, die natürlichen Zahlen oder so, aber es ist:

https://oeis.org/A000001 - Anzahl Gruppen der Ordnung n.

Tatsächlich eine interessante und wichtige Folge. Wer mal Gruppentheorie gelernt hat erinnert sich: Gruppen […]

Original post on mathstodon.xyz

49061132957714428902152118459264865645885092682687973 is an interesting number: it's the smallest integer not divisible by 2,3,5 or 7 and whose sum of proper divisors exceeds itself.

That's much bigger than I would have guessed!

A392235, "11-rough abundant numbers", just added to the #OEIS - […]

hellos everyones i am zoë trout i like these thingies and #math #maths #lisp #commonlisp #sbcl #seqfan #oeis #lambdamoo #lambda #calculus #mathypeopleswhonevercommentonparityexceptingcollatzobvsetc #emacs #fsf #gnu #number #theory #numbertheory #ethics #sex #primes #frozen and i apparently bluesky!.

A390774 - OEIS

Absolutely incredible addition to the #OEIS: numbers whose list digit is at most 3
https://oeis.org/A390774

Stick a decimal point before the last digit, and these are the possible heights of horses.

GitHub - hako/oeis-tui: A TUI and CLI for browsing the On-Line Encyclopedia of Integer Sequences (OEIS) in the terminal. A TUI and CLI for browsing the On-Line Encyclopedia of Integer Sequences (OEIS) in the terminal. - hako/oeis-tui

Wer von euch sich noch nicht so richtig mit graphischen Userinterfaces oder GUIs angefreundet hat, findet hier einen Text-Browser für die #OEIS:

https://github.com/hako/oeis-tui

Math exploration in the terminal? Done. 🤝

🔢 oeis-tui — A TUI to browse and explore OEIS integer sequences.

💯 Supports live preview, multi-tab sequence details & fast searching.

🦀 Written in Rust & built with @ratatui.rs

⭐ GitHub: github.com/hako/oeis-tui

#rustlang #ratatui #tui #math #oeis

A103841 - OEIS

Had a thought in the shower for an integer sequence. Unsurprisingly, it's already in #OEIS: https://oeis.org/A103841
More surprisingly, it's finite!

(After a little bit of thought, I can see why)

Today I learnt:

If you inscribe and circumscribe a million-gon around a unit circle. The two areas would approximate pi to only 10 dp.

(In truth, the approximation is valid by equal truncated values, and actually needs a regular polygon with 1,006,284 sides)

#mathsky
#pi
#piapproximations
#oeis

A390248: Number of reducible simple Venn diagrams with n curves. 1, 1, 1, 1, 11, 157619. Follow the link in the post for the comments text.

Wow, that escalated quickly.

https://oeis.org/A390248

#OEIS

Example: Compute the determinant of a tri-diagonal matrix with all non-zero entries equal to 2.

The resulting formula: a_n = 2^n ( cos(frac(pi,3)n) + frac(1,sqrt(3)) sin(frac(pi,3)n)).

I just wanted to quickly typst an example for the lecture tomorrow and suddenly I'm on #oeis again: https://oeis.org/A088138

I think this sequence is the result of the tri-diagonal determinant of twos, but it does not appear in the OEIS comments at all! […]

[Original post on machteburch.social]

A page of mindless doodles of polygon arrangements

I am wondering if I have a problem with #oeis searching... It's becoming obsessive

#mathsky

A390487 - OEIS

oeis.org/A390487

My second sequence just dropped!

Numbers k with the property that k is the next number that cannot be expressed as a linear sum of the squares of any of the preceding terms

Very happy with that.

1, 2, 6, 7, 11, 15, 21, 25, 61, 106, 142, 155, 515, 551, 36208...

#mathsky
#oeis

It turns out it's really hard to draw #Isometric paper by hand.

My teacher always told me I wouldn't walk around with a protractor in my pocket, and it turns out she was right.

In other news, I might have discovered a new #OEIS

Spoiler: 1, 6, 18, 45, 87

#mathsky

OEIS entry. https://oeis.org/A011545

I do love it when I am browsing the #OEIS and I find a comment that was within the last few weeks. Oddly titillating to know that someone else passed this way so recently.

oeis.org/A011545

#mathsky

I forget how crazy the stuff my kids come up with is. Luca just came up with this sequence - convert decimal digits of a number to binary then whole thing back to decimal - on his own. Wasn't surprised to see it was already in the #oeis. Couldve got one more in before he turns 6!

Me all weekend: "why have no #OEIS editors commented on my draft sequence?"

Me just now: *notices the button ""these edits are ready for review"*

Original post on mathstodon.xyz

I've just come up with a sequence I can't believe isn't in the #OEIS (#ICBINIOEIS)!

Take cards labelled 1 ... N. Shuffle them.

Repeat this procedure: look at the top card's value, X. Move X cards from the top of the deck to the back, one at a time.

If you ever end up back at your first card […]

#OEIS #wiki #Memoization #Python
https://oeis.org/wiki/Memoization#Python

Quelle est votre suite favorite de nombre entiers et pourquoi 2, 3, 4, 82000 ?
#OEIS