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 A185821 #10 Aug 04 2025 12:41:20 %S A185821 9,5680,1266624,378212944,100480040192,28043363244452, %T A185821 7662203273902712,2112817100467905536,580282378007177354752, %U A185821 159650092398206756238532,43890600560593534666234904,12070254095603726713513018032 %N A185821 1/5 the number of n X 5 0..4 arrays with every element equal to exactly one or two of its horizontal and vertical neighbors. %C A185821 Column 5 of A185825. %e A185821 Some solutions for 4 X 5 with a(1,1)=0 %e A185821 ..0..0..0..2..2....0..0..4..4..0....0..0..3..3..2....0..0..3..3..2 %e A185821 ..0..1..0..4..4....0..1..3..4..0....0..1..3..3..2....0..1..0..0..2 %e A185821 ..0..1..0..3..3....0..1..3..3..4....0..1..0..2..4....0..1..0..2..4 %e A185821 ..0..0..0..1..1....0..0..0..0..4....0..0..0..2..4....0..0..0..2..4 %Y A185821 Cf. A185825. %K A185821 nonn %O A185821 1,1 %A A185821 _R. H. Hardin_, Feb 05 2011