login
A181278
Number of 2 X n binary matrices M with rows in strictly increasing order and rows of M*Mtranspose (mod 2) in strictly decreasing order.
1
0, 3, 11, 48, 188, 768, 3056, 12288, 49088, 196608, 786176, 3145728, 12581888, 50331648, 201322496, 805306368, 3221209088, 12884901888, 51539542016, 206158430208, 824633458688, 3298534883328, 13194138484736, 52776558133248
OFFSET
1,2
COMMENTS
Row 2 of A181274.
LINKS
FORMULA
Empirical (for n>=2): 3*4^(n-2) + ((-1)^n-1)*2^(n-4). - Vaclav Kotesovec, Nov 27 2012
Conjectures from Colin Barker, Mar 27 2018: (Start)
G.f.: x^2*(3 - x - 8*x^2) / ((1 - 2*x)*(1 + 2*x)*(1 - 4*x)).
a(n) = 4*a(n-1) + 4*a(n-2) - 16*a(n-3) for n>3.
(End)
EXAMPLE
M and M*Mtranspose (mod 2) for 2 X 3:
..0..1..0......1..1
..0..1..1......1..0
CROSSREFS
Cf. A181274.
Sequence in context: A191344 A374983 A308538 * A126180 A121139 A316703
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 10 2010
STATUS
approved