%N Total number of ON cells after n generations of cellular automaton on triangular grid, starting from a node, in which every 60-degree wedge looks like the Sierpiński's triangle.
%C Analog of A160720, but here we are working on the triangular lattice.
%C The first differences (A256257) gives the number of triangular cells turned ON at every generation.
%C Also 6 times the sum of all entries in rows 0 to n of Sierpiński's triangle A047999.
%C Also 6 times the total number of odd entries in first n rows of Pascal's triangle A007318, see formula section.
%C The structure contains three distinct kinds of polygons formed by triangular ON cells: the initial hexagon, rhombuses (each one formed by two ON cells) and unit triangles.
%C Note that if n is a power of 2 greater than 2, the structure looks like concentric hexagons with triangular holes, where some of them form concentric stars.
%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>
%F a(n) = 6*A006046(n).
%e On the infinite triangular grid we start with all triangular cells turned OFF, so a(0) = 0.
%e At stage 1, in the structure there are six triangular cells turned ON forming a regular hexagon, so a(1) = 6.
%e At stage 2, there are 12 new triangular ON cells forming six rhombuses around the initial hexagon, so a(2) = 6 + 12 = 18.
%e And so on.
%o (PARI) a(n) = 6*sum(j=0, n, sum(k=0, j, binomial(j, k) % 2)); \\ _Michel Marcus_, Apr 01 2015
%Y Cf. A001316, A006046, A007318, A025192, A047999, A151723, A160120, A160720, A161644, A256257.
%A _Omar E. Pol_, Mar 20 2015