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 A220478 #21 Jul 07 2023 14:49:59 %S A220478 0,2,4,6,10,12,16,20,24,30,34,40,48,50,54,58,64,74,80,94,102,112,126, %T A220478 134,146,160,164,172,180,190,206,218,240,256,272,290,302,316,332,348, %U A220478 364,374,386,406,420,442,464,482,500,524,542,570,588,608,636,658,686,706,724,742 %N A220478 Equilateral triangle from the snowflake (or E-toothpick) structure of A161330 (see Comments lines for definition). %C A220478 It appears that if n >> 1 the structure looks like an equilateral triangle, which is essentially one of the six wedges of the E-toothpick (or snowflake) structure of A161330. The sequence gives the number of E-toothpicks in the structure after n stages. A220498 (the first differences) gives the number added at the n-th round. For more information and some illustrations see A161330. For the E-toothpick right triangle see A211964. %H A220478 N. J. A. Sloane, <a href="/A161330/a161330.jpg">A single E-toothpick</a> %H A220478 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 A220478 <a href="/index/Ce#cell">Index entries for sequences related to cellular automata</a> %H A220478 <a href="/index/To#toothpick">Index entries for sequences related to toothpick sequences</a> %F A220478 a(n) = n + (A161330(n) - 2)/6, n >= 1. %F A220478 a(n) = n + A161336(n) = 2*A211964(n). %Y A220478 Cf. A139250, A161328, A160120, A161330, A161336, A211964, A213360, A220498. %K A220478 nonn %O A220478 0,2 %A A220478 _Omar E. Pol_, Dec 22 2012