%I #9 May 17 2020 01:41:17
%S 1,1,3,19,379,22506,4063437,2303397986,4165684145897,
%T 24351094470461293,465231630106636264261,29310412705455253400706632,
%U 6135104108066245513806738233622,4293669524764808720927311131475805624,10102086274414407316013385512463577654333437
%N Number of lower triangles of an n X n 0..3 array with all row sums equal to the length of the row and all column sums equal to the length of the column.
%e Some solutions for n=4:
%e ..1........1........1........1........1........1........1........1
%e ..0.2......0.2......1.1......2.0......2.0......0.2......0.2......1.1
%e ..0.1.2....3.0.0....2.0.1....1.2.0....1.0.2....2.1.0....3.0.0....2.0.1
%e ..3.0.0.1..0.1.2.1..0.2.1.1..0.1.2.1..0.3.0.1..1.0.2.1..0.1.2.1..0.2.1.1
%Y Column 3 of A195644.
%K nonn
%O 1,3
%A _R. H. Hardin_, Sep 21 2011
%E a(12)-a(15) from _Andrew Howroyd_, May 16 2020