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.

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

R. H. Hardin, Table of n, a(n) for n=1..200

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: A295833 A191344 A308538 * A126180 A121139 A316703

Adjacent sequences: A181275 A181276 A181277 * A181279 A181280 A181281

Keyword

nonn

Author

R. H. Hardin, Oct 10 2010

Status

approved