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 A364487 #10 Aug 06 2023 11:55:24
%S A364487 1,0,1,0,2,1,5,2,13,5,36,16,96,45,262,128,720,368,1991,1047,5549,2995,
%T A364487 15583,8607,44027,24788,125043,71620,356706,207412,1021318,601719,
%U A364487 2933861,1748874,8452723,5091776,24417793,14848210,70706750,43364962,205193316,126828277
%N A364487 Number of fixed triangular n-ominoes of the regular tiling with Schläfli symbol {3,6} that have a common axis of symmetry coincident with cell altitudes and the point of the polyomino farthest along that axis in a specified direction is a cell edge center.
%C A364487 This is one of three sequences used to calculate A030223, the number of achiral polyominoes for this tiling. Two fixed polyominoes are identical only if one is a translation of the other.
%H A364487 Robert A. Russell, <a href="/A364487/b364487.txt">Table of n, a(n) for n = 1..60</a>
%F A364487 a(n) = 2*A030223(n) - A364486(n), n odd.
%F A364487 a(n) = 2*A030223(n) - A364485(n/2) - A364486(n), n even.
%e A364487 These are the n-ominoes for n<7. The highest point of the polyomino on the vertical axis of symmetry must be an edge center.
%e A364487 ____ ____ ____________ ____ ____
%e A364487 \ / /\ /\ \ /\ /\ / /\ /\ /\ /\
%e A364487 \/ /__\/__\ \/__\/__\/ /__\/__\ /__\/__\
%e A364487 \ /\ / \ /\ /
%e A364487 \/ \/ \/__\/
%Y A364487 Cf. A030223, A364485, A364486.
%K A364487 nonn
%O A364487 1,5
%A A364487 _Robert A. Russell_, Jul 26 2023