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 A047939 #13 Jun 18 2023 01:48:30 %S A047939 1,4,70,65824,1073758336,281474993496064,1180591620734591303680, %T A047939 79228162514264619068554215424,85070591730234615870455337878516924416, %U A047939 1461501637330902918203686041642102636484130504704,401734511064747568885490523085607563280607806359022338048000 %N A047939 Number of 4-colorings of an n X n grid, up to rotational symmetry. %H A047939 Andrew Howroyd, <a href="/A047939/b047939.txt">Table of n, a(n) for n = 0..25</a> %F A047939 a(n) = (m^(n^2) + 2 m^((n^2 + 3 (n mod 2))/4) + m^((n^2 + (n mod 2))/2))/4, with m = 4. %Y A047939 Column k=4 of A343095. %Y A047939 Cf. A054751, A047937. %K A047939 nonn %O A047939 0,2 %A A047939 _Rob Pratt_ %E A047939 Terms a(10) and beyond from _Andrew Howroyd_, Apr 14 2021