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 #5 Dec 18 2015 18:18:06
%S 1,2,24,616,34972,4448872,1271872472,816403740024,1175380974129748,
%T 3797950184579806600,27543816778839681854992,
%U 448288796291335397449297608
%N Number of n X n 0..2 symmetric matrices with every element equal to zero, one or three horizontal and vertical neighbors, and new values 0..2 introduced in lower triangle row major order
%e Some solutions for n=4
%e ..0..1..1..2....0..1..0..1....0..1..1..1....0..1..0..2....0..1..2..0
%e ..1..0..2..0....1..1..1..2....1..2..1..2....1..1..1..2....1..0..2..1
%e ..1..2..2..2....0..1..0..1....1..1..0..2....0..1..2..0....2..2..1..0
%e ..2..0..2..0....1..2..1..2....1..2..2..1....2..2..0..1....0..1..0..1
%K nonn
%O 1,2
%A _R. H. Hardin_ Mar 29 2012