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 A057785 #26 Feb 18 2023 07:29:47 %S A057785 0,1,2,1,1,4,4,10,13,31,43,102 %N A057785 Erroneous version of A355562. %C A057785 It would be nice to have a definition of "polypon"! - _N. J. A. Sloane_, May 09 2007 %C A057785 By looking at the Clarke pictures, I guess that the unit element is a triangle with internal angles of 120 degrees and two of 30 degrees. The polypons are connected, nonoverlapping assemblies of these, where connectivity is defined via common sides; a common point is not enough. Only non-congruential assemblies are counted, those which cannot be mapped onto each other by rotations, translations or mirrors along a line or point. However, the polypons are not all of these, because some of the free-form assemblies of this kind would need placement of the unit that violates the format by the grid. (The first case where this happens is with assemblies of 3 units: the picture shows 2 examples with assemblies of 3 units, but I can imagine at least 1 more where the unit would need to hide/cover one of the grid's edges.) - _R. J. Mathar_, Dec 10 2007 %D A057785 Computed by Brendan Owen. %H A057785 Andrew Clarke, <a href="http://www.recmath.com/PolyPages/PolyPages/PolyX/PolyX.htm">Other Polyforms</a> %Y A057785 Cf. A057784, A057786, A355562 (corrected version). %K A057785 dead %O A057785 1,3 %A A057785 _N. J. A. Sloane_, Nov 04 2000 %E A057785 Link updated by _William Rex Marshall_, Dec 16 2009