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 A216598 #42 Sep 07 2023 23:34:18 %S A216598 1,2,16,164,1866,22518,282184,3630256,47614214,633835642,8537220172 %N A216598 Number of distinct connected planar figures that can be formed from n 1 X 2 rectangles (or dominoes). %C A216598 "Connected" means "connected by edges". %C A216598 Rotations and reflections are considered different (cf. A056786). %C A216598 Internal arrangement of dominoes is significant (cf. A056785). - _Aaron N. Siegel_, May 22 2022 %H A216598 Manfred Scheucher, <a href="/A216598/a216598.sage.txt">Sage Script</a>. %H A216598 N. J. A. Sloane, <a href="/A056786/a056786.jpg">Illustration of initial terms of A056786, A216598, A216583, A216595, A216492, A216581</a>. %H A216598 N. J. A. Sloane, <a href="/A056786/a056786.pdf">Illustration of third term of A056786, A216598, A216583, A216595, A216492, A216581</a> (a better drawing for the third term). %H A216598 M. Vicher, <a href="http://www.vicher.cz/puzzle/polyforms.htm">Polyforms</a>. %H A216598 <a href="/index/Do#domino">Index entries for sequences related to dominoes</a> %Y A216598 Cf. A056786, A216598, A216583, A216595, A216492, A216581. %K A216598 nonn,more,nice,hard %O A216598 0,2 %A A216598 _N. J. A. Sloane_, Sep 09 2012 %E A216598 a(4) found via equivalence class decomposition over bounding boxes by the Forest Grove Community School Math Club - _Markus J. Q. Roberts_, Apr 03 2013 %E A216598 a(5)-a(9) from _Manfred Scheucher_, Jun 06 2015 %E A216598 a(10) from _Aaron N. Siegel_, May 22 2022