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 A186853 #13 Jan 07 2023 20:10:47 %S A186853 16,208,976,2576,5056,8320,12368,17200,22816,29216,36400,44368,53120, %T A186853 62656,72976,84080,95968,108640,122096,136336,151360,167168,183760, %U A186853 201136,219296,238240,257968,278480,299776,321856,344720,368368,392800 %N A186853 Number of 4-step knight's tours on an (n+2) X (n+2) board summed over all starting positions. %H A186853 Andrew Howroyd, <a href="/A186853/b186853.txt">Table of n, a(n) for n = 1..1000</a> %F A186853 Empirical: a(n) = 392*n^2 - 1048*n + 496 for n > 3. %F A186853 The above empirical formula is correct. See A186851 for details. - _Andrew Howroyd_, Jan 07 2023 %e A186853 Some solutions for 5 X 5: %e A186853 0 1 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 1 0 0 %e A186853 0 0 3 0 0 0 0 0 0 0 0 0 0 0 1 4 0 0 0 2 %e A186853 2 0 0 0 4 4 0 2 0 0 4 0 0 0 0 0 0 3 0 0 %e A186853 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 %e A186853 0 0 0 0 0 0 0 0 1 0 0 3 0 0 0 0 0 0 0 0 %o A186853 (PARI) row(4, 30) \\ row(m, n) defined in A186851. - _Andrew Howroyd_, Jan 07 2023 %Y A186853 Row 4 of A186851. %K A186853 nonn %O A186853 1,1 %A A186853 _R. H. Hardin_, Feb 27 2011