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 A208875 #7 Jul 22 2025 21:33:10 %S A208875 15,1979,324682,52947540,8624977114,1404920207834,228847686794351, %T A208875 37277070892199501,6072074518379364073,989082262060956074133, %U A208875 161111942886719306980432,26243578660069203997974518 %N A208875 Number of 4Xn 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 right-upward antidiagonal neighbors. %C A208875 Row 4 of A208872 %H A208875 R. H. Hardin, <a href="/A208875/b208875.txt">Table of n, a(n) for n = 1..210</a> %F A208875 Empirical: a(n) = 222*a(n-1) -10949*a(n-2) +228692*a(n-3) -2273610*a(n-4) +10170544*a(n-5) -13839646*a(n-6) -45418980*a(n-7) +225253855*a(n-8) -439046430*a(n-9) +509809347*a(n-10) -407061936*a(n-11) +239595084*a(n-12) -96068592*a(n-13) +18662400*a(n-14) for n>16 %e A208875 Some solutions for n=4 %e A208875 ..0..1..1..1....0..0..1..0....0..1..1..0....0..0..0..1....0..0..0..0 %e A208875 ..0..0..0..1....2..2..1..1....0..0..2..0....1..1..2..0....1..1..1..0 %e A208875 ..1..1..0..0....3..2..0..1....1..2..1..1....0..1..1..3....0..0..1..1 %e A208875 ..0..1..1..1....0..3..3..1....3..1..0..0....3..0..3..1....1..0..0..2 %K A208875 nonn %O A208875 1,1 %A A208875 _R. H. Hardin_ Mar 02 2012