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 A161421 #9 Feb 24 2021 02:48:18 %S A161421 0,1,2,2,2,4,8,6,6,8,12,8,10,10,20,18,10,16,20,8 %N A161421 First differences of A161420. %C A161421 Number of V-toothpicks added at the n-th stage to the V-toothpick structure of A161420. See also A161206 and A161207. %C A161421 Also it appears a(n) is also the number of toothpicks and D-toothpicks added at n-th stage to the H-toothpick structure of A161420. See also A182838 and A182839. %H A161421 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 A161421 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> %H A161421 <a href="/index/To#toothpick">Index entries for sequences related to toothpick sequences</a> %Y A161421 Cf. A139251, A161206, A161207, A161420, A161422, A182633, A182838, A182839. %K A161421 more,nonn %O A161421 0,3 %A A161421 _Omar E. Pol_, Jun 10 2009, Dec 12 2010