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 A197050 #13 Oct 24 2024 03:13:59 %S A197050 3,6,18,42,108,274,692,1754,4442,11248,28488,72146,182712,462728, %T A197050 1171876,2967826,7516146,19034954,48206826,122085820,309187486, %U A197050 783030352,1983057390,5022176478,12718873752,32211084212,81575929322,206594481604 %N A197050 Number of nX4 0..4 arrays with each element equal to the number its horizontal and vertical zero neighbors. %C A197050 Every 0 is next to 0 0's, every 1 is next to 1 0's, every 2 is next to 2 0's, every 3 is next to 3 0's, every 4 is next to 4 0's. %C A197050 Column 4 of A197054. %H A197050 R. H. Hardin, <a href="/A197050/b197050.txt">Table of n, a(n) for n = 1..210</a> %F A197050 Empirical: a(n) = a(n-1) +3*a(n-2) +3*a(n-3) -a(n-4) -2*a(n-5) -a(n-6) for n>7. %F A197050 Equivalent empirical g.f.: 3*x - 2*x^2*(1+x)*(x^4+3*x^3-3*x-3) / ( 1-x-3*x^2-3*x^3+x^4+2*x^5+x^6 ). - _R. J. Mathar_, Oct 10 2011 %e A197050 Some solutions for n=5 %e A197050 ..0..2..1..0....2..0..3..0....0..3..0..2....2..0..3..0....0..3..0..1 %e A197050 ..3..0..2..1....0..4..0..3....3..0..4..0....0..4..0..3....2..0..2..1 %e A197050 ..0..4..0..2....2..0..4..0....0..4..0..2....3..0..3..0....1..1..2..0 %e A197050 ..3..0..4..0....1..2..0..3....3..0..2..1....0..2..1..1....0..3..0..3 %e A197050 ..0..3..0..2....0..1..2..0....0..2..1..0....1..1..0..1....2..0..3..0 %K A197050 nonn %O A197050 1,1 %A A197050 _R. H. Hardin_, Oct 09 2011