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 A269047 #7 Jan 18 2019 15:21:26 %S A269047 24,102,594,3258,17346,90450,464250,2353338,11809746,58773858, %T A269047 290465706,1426996746,6974700162,33938314674,164494914138, %U A269047 794524032090,3825755303730,18370501130754,87990608484618,420498562000554 %N A269047 Number of n X 3 0..2 arrays with some element plus some horizontally, diagonally or antidiagonally adjacent neighbor totalling two not more than once. %H A269047 R. H. Hardin, <a href="/A269047/b269047.txt">Table of n, a(n) for n = 1..210</a> %F A269047 Empirical: a(n) = 10*a(n-1) - 29*a(n-2) + 20*a(n-3) - 4*a(n-4) for n>5. %F A269047 Empirical g.f.: 6*x*(1 - x)*(1 - 2*x)*(4 - 11*x + 4*x^2) / (1 - 5*x + 2*x^2)^2. - _Colin Barker_, Jan 18 2019 %e A269047 Some solutions for n=4: %e A269047 ..2..1..2. .1..2..0. .1..2..2. .1..2..2. .2..1..0. .0..0..0. .0..0..0 %e A269047 ..2..1..2. .1..0..1. .1..0..1. .1..2..2. .0..1..2. .0..1..0. .0..0..0 %e A269047 ..2..1..0. .0..0..0. .0..0..1. .1..2..1. .2..1..2. .0..1..2. .1..0..1 %e A269047 ..2..2..2. .0..0..0. .1..0..0. .0..0..1. .2..2..0. .2..1..2. .1..2..2 %Y A269047 Column 3 of A269052. %K A269047 nonn %O A269047 1,1 %A A269047 _R. H. Hardin_, Feb 18 2016