The OEIS lives here:
Super useful resource.
Super useful resource.
There's a mildly humorous "How do you know" exchange where someone on HN quizzes the very person most likely to know:
It's nice to see they have a solid plans on how to keep the website running indefinitely.
“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.”
Which were you thinking of?
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]
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]
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]
My underlying point is your sequence was under-specified, and with no clear reason to pick your preferred answer over other answers.
Even knowing it's chemistry, three finite sequences which match your specification are:
2, 8, 18, 32, 18, 8, 2
2, 8, 18, 32, 21, 9, 2
2, 8, 18, 32, 32, 14, 2