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 A239821 #7 Jun 02 2025 09:32:42 %S A239821 11,113,1480,18728,232272,2912793,36627126,459870638,5774508494, %T A239821 72538478424,911227478673,11446501405086,143789611879946, %U A239821 1806288798172920,22690641341877163,285040443527806965 %N A239821 Number of 3Xn 0..3 arrays with no element equal to zero plus the sum of elements to its left or one plus the sum of the elements above it, modulo 4. %C A239821 Row 3 of A239819 %H A239821 R. H. Hardin, <a href="/A239821/b239821.txt">Table of n, a(n) for n = 1..210</a> %H A239821 R. H. Hardin, <a href="/A239821/a239821.txt">Empirical recurrence of order 64</a> %F A239821 Empirical recurrence of order 64 (see link above) %e A239821 Some solutions for n=4 %e A239821 ..2..0..0..3....3..2..2..0....2..0..0..0....3..2..0..0....3..2..3..2 %e A239821 ..1..2..0..1....2..0..0..0....1..3..2..0....1..0..0..0....3..2..2..0 %e A239821 ..3..1..3..0....3..1..1..2....2..3..2..2....3..2..3..2....1..3..3..1 %K A239821 nonn %O A239821 1,1 %A A239821 _R. H. Hardin_, Mar 27 2014