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 A297870 #4 Jan 07 2018 11:28:02 %S A297870 0,1,3,2,11,13,34,65,123,266,499,1037,2042,4089,8219,16338,32827, %T A297870 65485,131090,262193,524155,1048794,2096899,4194509,8388586,16776937, %U A297870 33555099,67107874,134218827,268434701,536870786,1073743393,2147480443,4294971818 %N A297870 Number of nX2 0..1 arrays with every element equal to 2, 3 or 5 king-move adjacent elements, with upper left element zero. %C A297870 Column 2 of A297876. %H A297870 R. H. Hardin, <a href="/A297870/b297870.txt">Table of n, a(n) for n = 1..210</a> %F A297870 Empirical: a(n) = a(n-1) +3*a(n-2) -4*a(n-4) %e A297870 Some solutions for n=7 %e A297870 ..0..0. .0..0. .0..0. .0..0. .0..0. .0..0. .0..0. .0..0. .0..0. .0..0 %e A297870 ..0..0. .0..0. .0..0. .0..0. .1..0. .0..0. .0..0. .1..0. .1..0. .1..0 %e A297870 ..0..0. .1..1. .1..1. .1..1. .1..1. .1..1. .1..1. .1..1. .1..1. .1..1 %e A297870 ..0..0. .1..1. .1..0. .1..1. .1..0. .1..0. .1..1. .0..0. .0..1. .0..0 %e A297870 ..0..0. .1..1. .0..0. .0..0. .0..0. .0..0. .1..1. .0..0. .0..0. .0..0 %e A297870 ..1..1. .1..1. .1..0. .0..1. .0..1. .1..1. .0..0. .0..0. .1..0. .1..1 %e A297870 ..1..1. .1..1. .1..1. .1..1. .1..1. .1..1. .0..0. .0..0. .1..1. .1..1 %Y A297870 Cf. A297876. %K A297870 nonn %O A297870 1,3 %A A297870 _R. H. Hardin_, Jan 07 2018