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 A057784 #28 Feb 16 2025 08:32:43 %S A057784 1,2,2,4,4,10,13,29,47,100,181,383,738,1539,3087,6419,13135,27402, %T A057784 56779,118876,248384,521850,1096261,2310793,4874305,10305560,21810868, %U A057784 46239224 %N A057784 Number of polypons with n cells. %C A057784 A polypon is a polyform made up of 30-30-120 triangles from the [3.12^2] Laves tiling, joined along their edges. Because that tiling contains hexagons formed as a union of six triangles, with the division of the hexagon having less symmetry than the hexagon on its own, some polypons can be divided into their constituent triangles in more than one way, and whether the division is significant affects the values of a(n) when n >= 18 is a multiple of 6. For the present sequence, the division into triangles is considered significant. - _Joseph Myers_, Oct 02 2011 %D A057784 Computed by Brendan Owen. %H A057784 Andrew Clarke, <a href="http://www.recmath.com/PolyPages/PolyPages/PolyX/index.htm?PolyX.htm">Other Polyforms</a> %H A057784 Ed Pegg, Jr., <a href="http://demonstrations.wolfram.com/PolyformExplorer/">Illustrations of polyforms</a> %H A057784 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Polypon.html">Polypon</a> [From _Eric W. Weisstein_, Apr 24 2009] %Y A057784 Cf. A355562, A151531, A151532, A151533. %K A057784 nonn,nice,hard,more %O A057784 1,2 %A A057784 _N. J. A. Sloane_, Nov 04 2000 %E A057784 Link updated by _William Rex Marshall_, Dec 16 2009 %E A057784 a(21)-a(26) from _Joseph Myers_, Oct 02 2011 %E A057784 a(27)-a(28) from _Sean A. Irvine_, Jul 04 2022