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 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 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified August 13 04:54 EDT 2020. Contains 336442 sequences. (Running on oeis4.)