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 A364684 #10 Aug 04 2023 02:58:43
%S A364684 1,1,1,1,3,4,7,9,16,22,46,63,121,167,455,912,1263,2535,3514,7099,9873,
%T A364684 20043,27956,56807,79397,161736,226559,462482,649100,1327165,1865833,
%U A364684 3820605,5379507,11028753,15550459,31913892,45057416,92557088,130837407,268988726
%N A364684 Number of achiral triangular polyominoes with 6n cells and sixfold rotational symmetry.
%C A364684 These are polyominoes of the regular tiling with Schläfli symbol {3,6}. Their center is a vertex. As their symmetry group of order 12 is maximal, we can consider them either fixed, oriented (one-sided), or unoriented (free).
%H A364684 Robert A. Russell, <a href="/A364684/b364684.txt">Table of n, a(n) for n = 1..53</a>
%e A364684 ________ ________
%e A364684 /\ /\ /\ /\ /\ /\ /\
%e A364684 ____ ____/__\____ /__\/__\/__\ /__\/__\/__\
%e A364684 /\ /\ \ /\ /\ / /\ / \ /\ /\ /\ /\ /\
%e A364684 /__\/__\ \/__\/__\/ /__\/ \/__\ /__\/__\/__\/__\
%e A364684 \ /\ / /\ /\ /\ \ /\ /\ / \ /\ /\ /\ /
%e A364684 \/__\/ /__\/__\/__\ \/__\____/__\/ \/__\/__\/__\/
%e A364684 \ / \ /\ /\ / \ /\ /\ /
%e A364684 \/ \/__\/__\/ \/__\/__\/
%Y A364684 Cf. A006534 (oriented), A000577 (unoriented), A030224 (chiral), A030223 (achiral), A001420 (fixed).
%K A364684 nonn
%O A364684 1,5
%A A364684 _Robert A. Russell_, Aug 02 2023