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 A208411 #7 Dec 31 2023 15:40:23 %S A208411 15,2795,667478,163422914,40039156736,9810325806914,2403711876698218, %T A208411 588954110860577394,144304709913279198696,35357337571782719886214, %U A208411 8663205247528271356492160,2122646395773319892200238358 %N A208411 Number of 4 X n 0..3 arrays with new values 0..3 introduced in row major order and no element equal to more than two of its immediate leftward or upward or right-upward antidiagonal neighbors. %C A208411 Row 4 of A208408. %H A208411 R. H. Hardin, <a href="/A208411/b208411.txt">Table of n, a(n) for n = 1..210</a> %F A208411 Empirical: a(n) = 226*a(n-1) +4747*a(n-2) -18294*a(n-3) -739509*a(n-4) -1661510*a(n-5) +17227605*a(n-6) +10151090*a(n-7) -98711047*a(n-8) -11588022*a(n-9) +195980121*a(n-10) -44074854*a(n-11) -121060656*a(n-12) +71173728*a(n-13) -10077696*a(n-14) for n>16. %e A208411 Some solutions for n=4 %e A208411 ..0..0..0..1....0..1..0..0....0..1..1..1....0..0..0..0....0..0..0..1 %e A208411 ..1..2..1..1....2..0..3..0....0..0..0..1....0..1..1..2....0..1..1..0 %e A208411 ..0..2..0..3....2..0..3..1....0..1..0..0....1..0..1..3....0..1..1..0 %e A208411 ..0..0..2..1....1..2..0..2....0..1..1..1....1..3..3..1....0..0..0..1 %Y A208411 Cf. A208408. %K A208411 nonn %O A208411 1,1 %A A208411 _R. H. Hardin_, Feb 26 2012