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 A005396 M4043 #25 Jul 08 2025 16:30:27 %S A005396 1,0,0,6,0,30,24,168,288,1170,2760,9504,25776,84006,244104,779970, %T A005396 2356800,7487310,23167656,73639326,231348000,737718534,2341772136, %U A005396 7498417956,23982456384,77119604400,248088123192,800978437674,2588744704560,8388692108016,27217694697000 %N A005396 Number of 2n-step polygons on honeycomb. %D A005396 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A005396 M. E. Fisher and M. F. Sykes, <a href="http://dx.doi.org/10.1103/PhysRev.114.45">Excluded-volume problem and the Ising model of ferromagnetism</a>, Phys. Rev. 114 (1959), 45-58. %F A005396 a(n) = 2 * n * A006774(n), n > 1. - _Sean A. Irvine_, Aug 06 2020 %Y A005396 Cf. A001335. %K A005396 nonn %O A005396 2,4 %A A005396 _N. J. A. Sloane_ %E A005396 a(11)-a(21) from _Sean A. Irvine_, Jun 12 2016 %E A005396 a(0)-a(1) inserted and more terms from _Sean A. Irvine_, Aug 06 2020