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 A253771 #13 Jan 19 2015 23:27:51 %S A253771 0,6,18,18,54,18,54,54,126,54,54,54,126,90,126,162,306,162,54,54,126, %T A253771 90,126,162,306,198,126,162,306,306,342,414,702,486,126,54,126,90,126, %U A253771 162,306,198,126,162,306,306,342,414,702,522,198,162 %N A253771 First differences of A253770. %C A253771 Number of cells turned "ON" at n-th stage of cellular automaton of A253770. %C A253771 Also 6 times the number of Y-toothpicks added at n-th stage in the Y-toothpick structure of A160120. %H A253771 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 A253771 <a href="/index/Ce#cell">Index entries for sequences related to cellular automata</a> %F A253771 a(n) = 6*A160121(n). %e A253771 Positive terms can be written as a triangle in which row lengths is A011782 as shown below: %e A253771 6; %e A253771 18; %e A253771 18, 54; %e A253771 18, 54,54,126; %e A253771 54, 54,54,126,90,126,162,306; %e A253771 162, 54,54,126,90,126,162,306,198,126,162,306,306,342,414,702; %e A253771 486,126,54,126,90,126,162,306,198,126,162,306,306,342,414,702,522,198,162,... %Y A253771 Cf. A139251, A147582, A151724, A160121, A161645, A182633, A250301, A253770. %K A253771 nonn,tabf %O A253771 0,2 %A A253771 _Omar E. Pol_, Jan 13 2015