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 A201861 #21 May 30 2021 09:01:03 %S A201861 1,4,38,661,16286,527654,21191208,1015335608,56484795166, %T A201861 3576188894116,253756155257774,19937566770720487,1717714713900798962, %U A201861 160977153444563000938,16300053518916522372836,1773133639291617644092637,206197950879511078156507433 %N A201861 Number of ways to place n nonattacking ferses on an n X n board. %C A201861 Fers is a leaper [1,1]. %H A201861 V. Kotesovec, <a href="https://oeis.org/wiki/User:Vaclav_Kotesovec">Non-attacking chess pieces</a>, 6ed, 2013, p. 423. %F A201861 Asymptotic (Kotesovec, 2011): a(n) ~ n^(2n)/n!*exp(-5/2). %Y A201861 Cf. A201243 - A201248, A002465, A067965. %K A201861 nonn,hard %O A201861 1,2 %A A201861 _Vaclav Kotesovec_, Dec 06 2011 %E A201861 a(15) from _Vaclav Kotesovec_, Jan 03 2012 %E A201861 a(16) from _Vaclav Kotesovec_, Aug 31 2016 %E A201861 a(17) from _Vaclav Kotesovec_, May 30 2021