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 A356404 #15 Jul 14 2024 08:53:37 %S A356404 1,3,25,480,11997,350275,10780478 %N A356404 The number of closed routes of the chess knight, different in shape, consisting of 2 * n jumps on a checkered field without repeating cells of the route. %C A356404 Various closed routes of a chess knight on an unbounded checkered field are considered. The closed route of the chess knight means that with the last jump the chess knight returns to its original cell. A chess knight cannot jump into the same square twice. %C A356404 The first three members of the sequence were found by me manually, the remaining members were found by _Talmon Silver_ using a computer program. %H A356404 Nicolay Avilov, <a href="https://www.diofant.ru/problem/3580/">Problem 1820. Routes of the chess knight</a> (in Russian). %H A356404 Talmon Silver, <a href="/A356404/a356404.png">Nikoly Avilov's picture for a(3)</a> %e A356404 a(1)=1, since the only closed route for n=1 can be considered two jumps of a chess knight from any cell and back; %e A356404 a(2)=3 because the chess knight has 3 closed routes consisting of 4 jumps. We list them in the coordinate plane Oxy: %e A356404 1st route: (0;0), (1;2), (3;3), (2;1), (0;0); %e A356404 2nd route: (0;1), (1;3), (3;2), (2;0), (0;1); %e A356404 3rd route: (0;1), (2;2), (4;1), (2;0), (0;1). %Y A356404 Cf. A323131, A323559. %K A356404 nonn,walk,hard,more %O A356404 1,2 %A A356404 _Nicolay Avilov_, Aug 05 2022