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 A054361 #17 Dec 04 2023 06:40:12 %S A054361 0,0,0,0,0,0,3,20,198,1390,9474,35488,178448,696371,2721544,10683110, %T A054361 41334494,155723774,596182769,2257379379,8587521496,32688629235, %U A054361 124568505590,475147925759,1815832051949 %N A054361 Number of polyominoes with n cells without holes that do not tile the plane. %D A054361 Posting by Glenn C. Rhoads (rhoads(AT)paul.rutgers.edu) to rec.puzzles, Feb 17 2000. %H A054361 Craig S. Kaplan, <a href="https://isohedral.ca/heesch-numbers-of-unmarked-polyforms/">Heesch Numbers of Unmarked Polyforms</a> %H A054361 Craig S. Kaplan, <a href="https://arxiv.org/abs/2105.09438">Heesch Numbers of Unmarked Polyforms</a>, arXiv:2105.09438 [cs.CG], 2021. See Table 1 and Table 2. %H A054361 Joseph Myers, <a href="http://www.polyomino.org.uk/mathematics/polyform-tiling/">Polyomino tiling</a> %e A054361 a(7) = 3. %Y A054361 Cf. A000104, A054360, A070768, A071334. %K A054361 nonn,hard,more %O A054361 1,7 %A A054361 Joe Keane (jgk(AT)jgk.org) %E A054361 Corrected and extended by _Joseph Myers_, May 05 2002 %E A054361 More terms from _Joseph Myers_, Nov 04 2003 %E A054361 a(24) and a(25) from _Joseph Myers_, Nov 17 2010