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 A160123 #10 Feb 24 2021 02:48:18 %S A160123 1,1,3,1,3,3,7,3,3,3,7,5,7,9,17,9,3,3,7,5,7,9,17,11,7,9,17,17,19,23, %T A160123 39,27,7,3,7,5,7,9,17,11,7,9,17,17,19,23,39,29,11,9,17,17,19,25,43,39, %U A160123 25,23,39,45,47,57,93,77,23,3,7,5,7,9 %N A160123 a(n) = A160121(n+1)/3. %C A160123 Also, first differences of A161910. [From _Omar E. Pol_, Jun 21 2009] %H A160123 David Applegate, Omar E. Pol and N. J. A. Sloane, <a href="/A000695/a000695_1.pdf">The Toothpick Sequence and Other Sequences from Cellular Automata</a>, Congressus Numerantium, Vol. 206 (2010), 157-191. [There is a typo in Theorem 6: (13) should read u(n) = 4.3^(wt(n-1)-1) for n >= 2.] %H A160123 N. J. A. Sloane, <a href="/wiki/Catalog_of_Toothpick_and_CA_Sequences_in_OEIS">Catalog of Toothpick and Cellular Automata Sequences in the OEIS</a> %e A160123 Note that this can be written as a triangle: %e A160123 1; %e A160123 1; %e A160123 3; %e A160123 1,3; %e A160123 3,7,3,3; %e A160123 3,7,5,7,9,17,9,3; %e A160123 3,7,5,7,9,17,11,7,9,17,17,19,23,39,27,7; %e A160123 3,7,5,7,9,17,11,7,9,17,17,19,23,39,29,11,9,17,17,19,25,43,39,25,23,39,45,47,57,93,77,23; %e A160123 3,7,5,7,9,... %Y A160123 Y-toothpick sequence: A160120. Cf. A160121, A160122. %Y A160123 Cf. A139250, A139251. [From _Omar E. Pol_, Jun 16 2009] %Y A160123 Cf. A161831, A161427, A161910. [From _Omar E. Pol_, Jun 21 2009] %K A160123 nonn %O A160123 1,3 %A A160123 _Omar E. Pol_, May 02 2009, May 21 2010 %E A160123 More terms from _Omar E. Pol_, Jun 16 2009 %E A160123 Extended by _R. J. Mathar_, Feb 05 2010