Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #9 May 12 2023 15:08:06
%S 1,15,10682,163422914,39216100214432,146298576850884166522,
%T 8484183047877022205116428184,7648479804732030712438650610523878146,
%U 107185313935414834818609318544471943157967376388
%N Number of n X n 0..3 arrays with new values 0..3 introduced in row major order and no element equal to more than two of its immediate leftward or upward or right-upward antidiagonal neighbors.
%C Diagonal of A208408.
%H R. H. Hardin, <a href="/A208401/b208401.txt">Table of n, a(n) for n = 1..13</a>
%e Some solutions for n=4
%e ..0..1..1..2....0..0..0..1....0..1..0..0....0..1..1..0....0..0..1..0
%e ..0..1..0..0....0..1..1..0....2..0..3..0....0..0..2..0....2..0..1..2
%e ..0..0..3..0....0..1..1..0....2..0..3..1....0..2..1..1....1..3..0..0
%e ..1..1..2..0....0..0..0..1....1..2..0..2....3..1..0..0....1..3..2..2
%Y Cf. A208408.
%K nonn
%O 1,2
%A _R. H. Hardin_, Feb 26 2012