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 A209040 #9 Jul 22 2025 21:35:39 %S A209040 4,124,47700,225262148,13034933066892,9239962457023110368, %T A209040 80235179157233210417254036,8534774056580607728132307076396612, %U A209040 11121202754126311568095965858257048619933492 %N A209040 Number of n X n 0..3 arrays with no element equal the average of immediate neighbors vertically above and horizontally left of it. %C A209040 Diagonal of A209047 %H A209040 R. H. Hardin, <a href="/A209040/b209040.txt">Table of n, a(n) for n = 1..10</a> %e A209040 Some solutions for n=4 %e A209040 ..3..1..2..3....3..2..3..1....2..3..1..0....1..0..2..1....3..1..2..1 %e A209040 ..0..1..0..0....1..2..2..0....3..2..2..0....0..1..0..2....0..3..3..1 %e A209040 ..1..0..3..0....2..3..1..3....2..3..3..0....2..1..0..3....3..1..3..3 %e A209040 ..2..2..2..0....1..0..3..0....1..3..0..2....1..0..1..0....0..1..1..1 %K A209040 nonn %O A209040 1,1 %A A209040 _R. H. Hardin_ Mar 04 2012