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 A124997 #18 Dec 24 2016 11:14:43 %S A124997 0,0,0,25506,1759280998,854818404562894,3588226034666378581610, %T A124997 138311081613064367684548901556, %U A124997 50272239752141442901464758051467073726,174927321882862834702052846250836696969014873138,5889117928937174007411459040006660524033737246962655301188 %N A124997 Number of fault-free domino tilings (or dimer coverings) of a 2n X 2n square. %C A124997 Enumerates a subclass of the things counted by A004003. %C A124997 "Fault-free" means that every straight line through the interior of the square hits the interior of some domino. %H A124997 Xu Mingkuan, <a href="/A124997/b124997.txt">Table of n, a(n) for n = 1..12</a> %Y A124997 Cf. A004003. %K A124997 nonn %O A124997 1,4 %A A124997 _Don Knuth_, Jun 26 2008 %E A124997 a(7) from _Alois P. Heinz_, Oct 19 2015 %E A124997 a(8)-a(11) from _Xu Mingkuan_, Dec 23 2016