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 A161836 #6 Feb 24 2021 02:48:18 %S A161836 0,0,0,0,3,3,3,3,9,15 %N A161836 Number of concave-convex hexagons in the Y-toothpick structure of A160120 after n rounds. %H A161836 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 A161836 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> %Y A161836 Cf. A139250, A160120, A160124, A161419, A161418, A161828, A161837. %K A161836 more,nonn %O A161836 0,5 %A A161836 _Omar E. Pol_, Jun 21 2009