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 A182563 #15 Jul 22 2025 08:44:15 %S A182563 1,6,70,1289,33864,1148760,47700972,2344465830,133055587660, %T A182563 8559364525414,615266768106190,48861588247978827,4247584874013608724, %U A182563 401107335066453376830,40880928693752664368224,4472281486633326131737868 %N A182563 Number of ways to place n non-attacking semi-knights on an n x n chessboard. %C A182563 Semi-knight is a semi-leaper [1,2]. Moves of a semi-knight are allowed only in [2,1] and [-2,-1]. See also semi-bishops (A187235). %H A182563 V. Kotesovec, <a href="https://oeis.org/wiki/User:Vaclav_Kotesovec">Non-attacking chess pieces</a>, 6ed, p.289 %F A182563 Asymptotic: a(n) ~ n^(2n)/n!*exp(-3/2). %Y A182563 Cf. A182562, A201540, A201513, A002465, A201511, A197989, A201861. %K A182563 nonn,hard,more %O A182563 1,2 %A A182563 _Vaclav Kotesovec_, May 05 2012 %E A182563 a(16) from _Vaclav Kotesovec_, May 24 2021