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 A209502 #7 Jul 22 2025 21:46:25 %S A209502 855,1920126,5801378991,17538444837670,53052739133301878, %T A209502 160472621147386212721,485400266057664024464791, %U A209502 1468244769479038501500597043,4441166748603271019044231589770 %N A209502 Number of nX7 0..4 arrays with every 2X2 subblock containing exactly one value repeat, and new values 0..4 introduced in row major order. %C A209502 Column 7 of A209503 %H A209502 R. H. Hardin, <a href="/A209502/b209502.txt">Table of n, a(n) for n = 1..124</a> %e A209502 Some solutions for n=4 %e A209502 ..0..0..0..0..0..0..0....0..0..0..0..0..0..0....0..0..0..1..0..1..2 %e A209502 ..1..2..3..4..1..4..1....1..2..1..2..1..2..1....2..1..2..0..2..0..2 %e A209502 ..4..1..2..4..3..3..3....0..0..2..3..1..3..1....3..1..3..3..0..1..0 %e A209502 ..0..4..4..3..0..4..0....2..1..0..0..1..4..1....2..3..2..0..1..2..1 %K A209502 nonn %O A209502 1,1 %A A209502 _R. H. Hardin_ Mar 09 2012