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 A208877 #7 Jul 22 2025 21:33:24 %S A208877 187,405481,808928836,1574432811027,3057224057476808, %T A208877 5935974611645510227,11525604443642285224422, %U A208877 22378818401741996203540140,43452103699438321679996424291,84369306929975201481569423835330 %N A208877 Number of 6Xn 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 A208877 Row 6 of A208872 %H A208877 R. H. Hardin, <a href="/A208877/b208877.txt">Table of n, a(n) for n = 1..56</a> %e A208877 Some solutions for n=4 %e A208877 ..0..1..2..3....0..1..0..0....0..0..0..1....0..0..0..0....0..1..1..0 %e A208877 ..0..1..2..0....2..2..1..2....2..3..2..0....1..1..1..0....0..0..1..1 %e A208877 ..0..1..3..0....1..2..3..2....1..2..1..1....0..0..1..1....1..0..2..1 %e A208877 ..2..0..3..0....0..3..0..0....1..0..2..1....1..0..0..2....1..1..0..3 %e A208877 ..2..0..3..1....1..3..2..1....3..3..1..2....3..1..1..2....2..3..0..0 %e A208877 ..1..2..0..2....1..2..1..2....0..2..3..1....0..2..0..0....0..2..1..3 %K A208877 nonn %O A208877 1,1 %A A208877 _R. H. Hardin_ Mar 02 2012