[jacquesm]

The OEIS lives here:

https://oeis.org/

Super useful resource.

[typical182]

As I understand it, written in Go.

There's a mildly humorous "How do you know" exchange where someone on HN quizzes the very person most likely to know:

https://news.ycombinator.com/item?id=9920020

[jacquesm]

HN has had a couple of those.

[recov]

Mandatory HN lore https://news.ycombinator.com/item?id=35079

[jacquesm]

That was one of the ones I had in mind. What's really neat is that everybody from that thread is still visiting HN and participating.

[totetsu]

Any website that lets me see "The numbers of Mozart's piano concerti" as a graph must be doing something correctly. http://oeis.org/A064172/graph

[ta123456789]

OEIS foundation:

http://oeisf.org/

It's nice to see they have a solid plans on how to keep the website running indefinitely.

[dahart]

Yes, I’m also glad to hear it’s future path is already paved. Sloane described the process and history in the paper:

“In 2009, in order to ensure the long-term future of the database, I set up a non-profit foundation, The OEIS Foundation Inc., a 501(c)(3) Public Charity, whose purpose is to own, maintain and raise funds to support The On-Line Encyclopedia of Integer Se- quences or OEIS.

On October 26, 2009, I transferred the intellectual property of The On-Line Ency- clopedia of Integer Sequences to the Foundation. A new OEIS with multiple editors was launched on November 11, 2010.

Since then it has been possible for anyone in the world to propose a new sequence or an update to an existing sequence. To do this, users must first register, and then submissions are reviewed by the editors before they become a permanent part of the OEIS. Technically the OEIS is now a “moderated wiki”.

I started writing this article on November 11, 2022, noting that this marked twelve years of successful operation of the online OEIS, and also that the database is in its 59th year of existence.”

[Aardwolf]

The one thing I wish is they had a keyword for base-ten related sequences (rather than only "base" for any base), because base ten related sequences simply are almost always going to be way more recreational maths related than base two or base three related sequences.

[yreg]

I always have a need to use this on puzzle hunts, but I don't think it ever helped.

[jacquesm]

Quick: 2, 8, 18, 32, ?? ?

[eesmith]

11 distinct answers on OEIS, assuming the 2 is either the first value, or you omitted an initial 0.

Which were you thinking of?

[jacquesm]

The 2 is the first value. And no spoilers.

[eesmith]

https://oeis.org/A001105 starts with 0 so I guess you don't mean that obvious quadratic.

Could be https://oeis.org/A209303 :

  def f(n):
    return n*n + sum(k*k for k in map(int, str(n)))

  >>> [f(i) for i in range(1, 5)]
  [2, 8, 18, 32]

but I don't know why that entry doesn't start with 0.

Could be https://oeis.org/A190787 :

  >>> import heapq, itertools
  >>> seq = heapq.merge((2**i for i in itertools.count(1, 2)),
              (9*2**i for i in itertools.count(1, 2)))
  >>> list(itertools.islice(seq, 0, 4))
  [2, 8, 18, 32]

Or https://oeis.org/A067051:

  import itertools

  def sigma(n):
    return sum(i for i in range(1, n//2+1) if n % i == 0)

  def seq():
    for n in itertools.count(1):
      if sigma(2*n) % 2 == 0: continue
      if sigma(3*n) % 3 == 0: yield n
      continue

  >>> list(itertools.islice(seq(), 0, 4))
  [2, 8, 18, 32]

The others are either degenerate for 4 points of the A001105 case, or are not so easy to implement in raw Python.

[jacquesm]

Think chemistry...

[webreac]

50. The best answer is the simplest one. IMHO, 2n^2 is very simple.