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 A006535 M2846 #51 Feb 16 2025 08:32:30 %S A006535 1,1,3,10,33,147,620,2821,12942,60639,286190,1364621,6545430,31586358, %T A006535 153143956,745700845,3644379397,17869651166,87877879487,433301253231, %U A006535 2141584454057,10607707971062,52646117638427,261756764824964,1303625908234997,6502430891223011,32480041218465452,162454295068924189,813541940383789255,4078750395194965720 %N A006535 Number of one-sided hexagonal polyominoes with n cells. %D A006535 J. Meeus, personal communication. %D A006535 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A006535 John Mason, <a href="/A006535/b006535.txt">Table of n, a(n) for n = 1..36</a> %H A006535 J. Meeus & N. J. A. Sloane, <a href="/A006532/a006532_1.pdf">Correspondence, 1974-1975</a> %H A006535 Ed Pegg, Jr., <a href="http://demonstrations.wolfram.com/PolyformExplorer/">Illustrations of polyforms</a> %H A006535 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Polyhex.html">Polyhex</a> %F A006535 a(n) = 2*A000228(n) - A030225(n). %Y A006535 Cf. A000228, A030225, A001207. %K A006535 nonn,hard,nice %O A006535 1,3 %A A006535 _N. J. A. Sloane_ %E A006535 a(7)-a(12) from _David W. Wilson_ %E A006535 a(13) from _Achim Flammenkamp_, Feb 15 1999 %E A006535 a(14)-a(20) from _Joseph Myers_, Sep 21 2002 %E A006535 a(21)-a(30) from _John Mason_, Jul 18 2023