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 A208860 #7 Jul 22 2025 21:31:47 %S A208860 15,1691,273049,44452082,7240366702,1179377179523,192108983085145, %T A208860 31292693945057258,5097277404701734234,830297232890575975631, %U A208860 135247396001465780031025,22030493903508619572329906 %N A208860 Number of nX4 0..3 arrays with new values 0..3 introduced in row major order and no element equal to more than one of its immediate leftward or upward or left-upward diagonal neighbors. %C A208860 Column 4 of A208864 %H A208860 R. H. Hardin, <a href="/A208860/b208860.txt">Table of n, a(n) for n = 1..210</a> %F A208860 Empirical: a(n) = 219*a(n-1) -10289*a(n-2) +197167*a(n-3) -1651023*a(n-4) +4615685*a(n-5) +5157645*a(n-6) -45444123*a(n-7) +78064236*a(n-8) -63363708*a(n-9) +40081392*a(n-10) -18662400*a(n-11) for n>12 %e A208860 Some solutions for n=4 %e A208860 ..0..0..1..0....0..0..1..2....0..0..0..0....0..1..1..0....0..0..0..1 %e A208860 ..0..2..2..0....0..3..3..0....1..1..1..1....0..1..2..0....1..1..1..2 %e A208860 ..2..3..3..0....1..0..1..2....2..2..2..3....0..2..1..1....2..2..2..0 %e A208860 ..1..2..0..2....1..2..0..0....0..1..3..0....3..1..0..0....0..3..0..1 %K A208860 nonn %O A208860 1,1 %A A208860 _R. H. Hardin_ Mar 02 2012