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 A283108 #18 Apr 15 2023 15:44:03 %S A283108 0,0,1,4,14,51,181,652,2356,8625,31791,118195,442261,1665299,6302903, %T A283108 23968090,91513682,350687935,1348198490,5198114444,20094107710, %U A283108 77860452105,302340714990,1176325327796,4584989069865,17900574971247,69993587545033,274071021159757,1074577571232370 %N A283108 Number of fixed polyominoes minus number of free polyominoes for order n. %C A283108 a(n) is the number of fixed polyominoes that are a transform -- except through identity -- of a canonical polyomino. %C A283108 E.g., n=3: %C A283108 A001168 %C A283108 ________|_________ %C A283108 | | %C A283108 A000105 | A283108 %C A283108 canon | transform %C A283108 | %C A283108 * | %C A283108 * | %C A283108 * | * * * %C A283108 | %C A283108 * | * * * * * %C A283108 * * | * * * * %H A283108 John Mason, <a href="/A283108/b283108.txt">Table of n, a(n) for n = 0..50</a> %F A283108 a(n) = A001168(n) - A000105(n). %Y A283108 Cf. A000105, A001168. %K A283108 nonn %O A283108 0,4 %A A283108 _Francois Alcover_, Feb 28 2017