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 A269030 #8 Jan 18 2019 09:58:15 %S A269030 12,48,348,2136,12228,67104,357756,1867560,9593844,48665904,244357740, %T A269030 1216672824,6015296484,29561944128,144531868764,703461546312, %U A269030 3410368965588,16475694411600,79347347565132,381071870841432 %N A269030 Number of n X 3 0..2 arrays with some element plus some horizontally, diagonally or antidiagonally adjacent neighbor totalling two exactly once. %H A269030 R. H. Hardin, <a href="/A269030/b269030.txt">Table of n, a(n) for n = 1..210</a> %F A269030 Empirical: a(n) = 10*a(n-1) - 29*a(n-2) + 20*a(n-3) - 4*a(n-4) for n>5. %F A269030 Empirical g.f.: 12*x*(1 - 6*x + 18*x^2 - 16*x^3 + 4*x^4) / (1 - 5*x + 2*x^2)^2. - _Colin Barker_, Jan 18 2019 %e A269030 Some solutions for n=4: %e A269030 ..1..2..2. .2..2..2. .1..0..2. .0..0..0. .2..2..1. .0..1..0. .2..1..0 %e A269030 ..2..2..2. .2..1..2. .1..2..1. .0..0..0. .1..2..2. .1..0..0. .0..1..2 %e A269030 ..2..1..0. .2..2..2. .2..2..1. .0..1..0. .2..2..1. .0..0..0. .0..1..0 %e A269030 ..2..1..0. .2..1..0. .2..2..1. .2..0..0. .2..1..2. .0..0..0. .0..0..2 %Y A269030 Column 3 of A269035. %K A269030 nonn %O A269030 1,1 %A A269030 _R. H. Hardin_, Feb 18 2016