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 A375209 #25 Nov 01 2024 21:37:24 %S A375209 1,2,16,564,93866,72054120,260324223938,4400423201461008, %T A375209 349815282628284276844,130501147375292529852604266, %U A375209 228964256366276749773274186140858 %N A375209 Number of simple symmetric Hamiltonian paths connecting opposite corners of a 2n+1 X 2n+1 grid. %H A375209 Nicolay Avilov, <a href="https://www.diofant.ru/problem/4531/">Problem 2718. Broken Routes</a> (in Russian). %H A375209 Nicolay Avilov, <a href="/A375209/a375209_1.jpg">Illustration for term a(2)</a> %F A375209 a(n) = 2*A331001(2*n + 1) for n > 0. - _Andrew Howroyd_, Oct 16 2024 %e A375209 a(2) = 16, see link "Illustration". %Y A375209 Cf. A001184, A331001. %K A375209 nonn,more %O A375209 0,2 %A A375209 _Nicolay Avilov_, Oct 16 2024 %E A375209 Thanks to Suleiman Makarenko. %E A375209 a(5)-a(10) from _Andrew Howroyd_, Oct 16 2024