This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A367609 #13 Feb 07 2024 13:21:43
%S A367609 11,21,1,-1,21,2,11,21,1,11,22,1,11,22,1,12,22,2,12,21,2,-1,21,2,11,
%T A367609 21,1,11,21,1,11,21,1,11,21,1,11,21,1,11,21,1,11,21,1,11,22,1,11,22,1,
%U A367609 12,22,2,12,22,2,12,22,2,12,22,2,12,22,2,12,22,2,12,22,2,12,21,2,-1,21,2,11,21,1,11,21,1,11,21,1,11,21,1,11,21,1,11,21,1,11,21,1,11
%N A367609 Comma-number associated with A367607(n), and written in base 3, or -1 if A367607(n) = -1.
%C A367609 This is a base-3 analog of A367339.
%H A367609 Michael S. Branicky, <a href="/A367609/b367609.txt">Table of n, a(n) for n = 1..10000</a>
%H A367609 Eric Angelini, Michael S. Branicky, Giovanni Resta, N. J. A. Sloane, and David W. Wilson, The Comma Sequence: A Simple Sequence With Bizarre Properties, <a href="http://arxiv.org/abs/2401.14346">arXiv:2401.14346</a>, <a href="https://www.youtube.com/watch?v=_EHAdf6izPI">Youtube</a>
%o A367609 (Python)
%o A367609 from sympy.ntheory.factor_ import digits
%o A367609 def a(n):
%o A367609 b = n + 3*(n%3)
%o A367609 return next((int("".join(map(str, digits(b+y-n, 3)[1:]))) for y in [1, 2] if digits(b+y, 3)[1] == y), -1)
%o A367609 print([a(n) for n in range(1, 101)]) # _Michael S. Branicky_, Dec 11 2023
%Y A367609 Cf. A121085, A367339, A367355, A367356, A367606-A367608.
%K A367609 sign,base
%O A367609 1,1
%A A367609 _N. J. A. Sloane_, Dec 11 2023