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 A229537 #8 Apr 27 2021 21:00:52 %S A229537 0,84,356,3064,19276,130854,833108,5305746,33122792,205196216, %T A229537 1258781344,7670081250,46440194380,279724889174,1677103031212, %U A229537 10014905982560,59591710277588,353467715910526,2090642805771012,12333845570879546 %N A229537 Number of defective 3-colorings of a 4 X n 0..2 array connected horizontally, diagonally and antidiagonally with exactly one mistake, and colors introduced in row-major 0..2 order. %C A229537 Row 4 of A229534. %H A229537 R. H. Hardin, <a href="/A229537/b229537.txt">Table of n, a(n) for n = 1..210</a> %F A229537 Empirical: a(n) = 6*a(n-1) + 23*a(n-2) - 102*a(n-3) - 288*a(n-4) + 250*a(n-5) + 787*a(n-6) - 238*a(n-7) - 741*a(n-8) + 124*a(n-9) + 196*a(n-10) - 16*a(n-11) - 16*a(n-12) for n > 14. %e A229537 Some solutions for n=4: %e A229537 0 1 0 1 0 1 0 2 0 1 0 1 0 1 0 1 0 1 0 2 %e A229537 0 1 0 2 2 1 0 1 0 2 0 2 2 1 0 1 0 1 0 1 %e A229537 0 2 1 2 0 2 0 1 1 2 1 2 0 1 0 1 2 1 0 2 %e A229537 1 2 1 0 0 2 0 2 0 2 0 0 2 2 0 2 0 2 0 1 %Y A229537 Cf. A229534. %K A229537 nonn %O A229537 1,2 %A A229537 _R. H. Hardin_, Sep 25 2013