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 A006774 M2257 #22 Sep 07 2022 14:55:59 %S A006774 1,0,0,1,0,3,2,12,18,65,138,432,1074,3231,8718,25999,73650,220215, %T A006774 643546,1937877,5783700,17564727,53222094,163009086,499634508, %U A006774 1542392088,4770925446,14832934031,46227584010,144632622552,453628244950 %N A006774 Number of 2n-step polygons on honeycomb. %D A006774 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A006774 I. Jensen, <a href="/A006774/b006774.txt">Table of n, a(n) for n = 0..79</a> %H A006774 I. G. Enting and A. J. Guttmann, <a href="https://www.researchgate.net/publication/230900049_Polygons_on_the_honeycomb_lattice">Polygons on the honeycomb lattice</a>, J. Phys. A 22 (1989), 1371-1384. %H A006774 I. Jensen, <a href="http://www.ms.unimelb.edu.au/~iwan/polygons/series/tri.perim.rgs.ser">More terms</a> %F A006774 a(n) = A005396(n) / (2*n), n > 1. - _Sean A. Irvine_, Aug 06 2020 %K A006774 nonn %O A006774 0,6 %A A006774 _N. J. A. Sloane_ %E A006774 a(0)-a(2) inserted by _Sean A. Irvine_, Aug 06 2020