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 A201513 #21 May 11 2017 17:46:08 %S A201513 1,1,0,8,79,1974,62266,2484382,119138166,6655170642,423677826986, %T A201513 30242576462856,2390359529372724,207127434998494421, %U A201513 19516867860507198208,1986288643031862123264,217094567491104327256049,25357029929230564723578520,3151672341378566296926684684 %N A201513 Number of ways to place n nonattacking kings on an n X n board. %H A201513 Alois P. Heinz, <a href="/A201513/b201513.txt">Table of n, a(n) for n = 0..21</a> (terms n=1..20 from Andrew Woods) %H A201513 V. Kotesovec, <a href="https://oeis.org/wiki/User:Vaclav_Kotesovec">Non-attacking chess pieces</a>, 6ed, 2013, p. 77. %F A201513 Asymptotics (Vaclav Kotesovec, Nov 29 2011): n^(2n)/n!*exp(-9/2). %Y A201513 Cf. A061995, A061996, A061997, A061998, A172158, A194788, A201369. %Y A201513 Cf. A063443. %Y A201513 Main diagonal of A098487, A193580. %K A201513 nonn,nice %O A201513 0,4 %A A201513 _Vaclav Kotesovec_, Dec 02 2011 %E A201513 a(0)=1 prepended by _Alois P. Heinz_, May 11 2017