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 A160426 #12 Feb 24 2021 02:48:18 %S A160426 0,5,9,17,30,42,52,69,90,102,112,129,150,170,196,237,274,286,296,313, %T A160426 334,354,380,421,458,478,504,545,590,642,724,829,898,910,920,937,958, %U A160426 978,1004,1045,1082,1102,1128,1169,1214 %N A160426 Toothpick sequence starting from an asymmetric cross, with four edges of length 1, 2, 3 and 4, formed by five toothpicks of length 2. %C A160426 On the infinite square grid we start at stage 0 with no toothpicks. At stage 1 we place three consecutive toothpicks and two orthogonal toothpicks, as an asymetric cross with four edges of length 1, 2, 3, and 4, then a(1)=5. At stage 2 we place 4 toothpicks. And so on... %C A160426 The sequence gives the number of toothpicks in the structure after n stages. A160427 (the first differences) gives the number added at the n-th stage. See A139250 for more information about toothpick sequences. %H A160426 Nathaniel Johnston, <a href="/A160426/b160426.txt">Table of n, a(n) for n = 0..455</a> %H A160426 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 A160426 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 A160426 Nathaniel Johnston, <a href="/A160426/a160426.c.txt">C program for computing terms</a> %Y A160426 Cf. A139250, A139251, A160740, A160800, A160802, A160808. %K A160426 nonn %O A160426 0,2 %A A160426 _Omar E. Pol_, May 25 2009, May 29 2009 %E A160426 Terms after a(13) from _Nathaniel Johnston_, Mar 31 2011