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 A187508 #16 Aug 23 2025 00:01:40 %S A187508 0,6,31,74,135,214,311,426,559,710,879,1066,1271,1494,1735,1994,2271, %T A187508 2566,2879,3210,3559,3926,4311,4714,5135,5574,6031,6506,6999,7510, %U A187508 8039,8586,9151,9734,10335,10954,11591,12246,12919,13610,14319,15046,15791 %N A187508 Number of 3-step S, E, and NW-moving king's tours on an n X n board summed over all starting positions. %H A187508 R. H. Hardin, <a href="/A187508/b187508.txt">Table of n, a(n) for n = 1..50</a> %F A187508 Empirical: a(n) = 9*n^2 - 20*n + 10 for n>1. %F A187508 Empirical g.f.: x^2*(6+13*x-x^2)/(1-x)^3. - _Colin Barker_, Jan 22 2012 %e A187508 Some solutions for 4X4 %e A187508 ..0..0..0..0....0..0..0..0....1..0..0..0....0..2..0..0....3..1..0..0 %e A187508 ..0..2..3..0....3..0..0..0....2..3..0..0....0..3..1..0....0..2..0..0 %e A187508 ..0..0..1..0....0..2..0..0....0..0..0..0....0..0..0..0....0..0..0..0 %e A187508 ..0..0..0..0....0..0..1..0....0..0..0..0....0..0..0..0....0..0..0..0 %Y A187508 Row 3 of A187507. %K A187508 nonn %O A187508 1,2 %A A187508 _R. H. Hardin_, Mar 10 2011