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 A213377 #13 Jul 09 2019 13:05:57 %S A213377 1,3,20,170,1728,18878,214278,2488176,29356463 %N A213377 Number of polyominoes of order 2n that can be tiled by dominoes in a unique way. %C A213377 Tilings related by a symmetry of the polyomino that is not a symmetry of the tiling count as distinct (thus, the square tetromino counts as being tiled in two distinct ways). %H A213377 Herman Tulleken, <a href="https://www.researchgate.net/publication/333296614_Polyominoes">Polyominoes 2.2: How they fit together</a>, (2019). %Y A213377 Cf. A056785, A056786, A213376, A213378. %K A213377 hard,more,nonn %O A213377 1,2 %A A213377 _Joseph Myers_, Jun 10 2012