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 A139560 #10 Feb 24 2021 02:48:18 %S A139560 1,2,2,2,4,4,2,2,4,4,4,8,12,8,2,2,4,4,4,8,12,8,4,8,12,12,16,28,32,16, %T A139560 2,2,4,4,4,8,12,8,4,8,12,12,16,28,32,16,4,8,12,12,16,28,32,20,16,28, %U A139560 36,40,60,88,80,32 %N A139560 Number of new segments added to the toothpick structure drawing at the n-th step (extensions of earlier segments are not considered). %C A139560 First differences of A139252. %H A139560 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 A139560 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> %F A139560 a(n)=A139252(n)-A139252(n-1). %Y A139560 Cf. A139250, A139251, A139252, A139253, A139254, A139559. %K A139560 nonn %O A139560 1,2 %A A139560 _Omar E. Pol_, May 17 2008 %E A139560 Terms after a(28) from _Nathaniel Johnston_, Mar 29 2011