A220478 - OEIS

%I #21 Jul 07 2023 14:49:59

%S 0,2,4,6,10,12,16,20,24,30,34,40,48,50,54,58,64,74,80,94,102,112,126,

%T 134,146,160,164,172,180,190,206,218,240,256,272,290,302,316,332,348,

%U 364,374,386,406,420,442,464,482,500,524,542,570,588,608,636,658,686,706,724,742

%N Equilateral triangle from the snowflake (or E-toothpick) structure of A161330 (see Comments lines for definition).

%C 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 N. J. A. Sloane, <a href="/A161330/a161330.jpg">A single E-toothpick</a>

%H 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 <a href="/index/Ce#cell">Index entries for sequences related to cellular automata</a>

%H <a href="/index/To#toothpick">Index entries for sequences related to toothpick sequences</a>

%F a(n) = n + (A161330(n) - 2)/6, n >= 1.

%F a(n) = n + A161336(n) = 2*A211964(n).

%Y Cf. A139250, A161328, A160120, A161330, A161336, A211964, A213360, A220498.

%K nonn

%O 0,2

%A _Omar E. Pol_, Dec 22 2012