A268973 Number of 3 X n 0..2 arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling two not more than once.

27, 336, 2016, 11664, 63792, 339480, 1770048, 9084744, 46050480, 231090264, 1150053408, 5683587048, 27921925008, 136471932792, 664055030016, 3218568401160, 15545839096944, 74855120204952, 359437016141280

Offset

1,1

Links

R. H. Hardin, Table of n, a(n) for n = 1..210

Formula

Empirical: a(n) = 10*a(n-1) - 29*a(n-2) + 20*a(n-3) - 4*a(n-4) for n>6.

Empirical g.f.: 3*x*(9 + 22*x - 187*x^2 + 236*x^3 - 332*x^4 + 280*x^5) / (1 - 5*x + 2*x^2)^2. - Colin Barker, Jan 17 2019

Example

Some solutions for n=4:
..1..2..1..0. .2..2..2..2. .1..2..2..2. .2..1..2..2. .0..1..2..2
..1..2..0..1. .2..2..1..0. .1..2..2..1. .0..0..1..2. .0..1..2..1
..1..0..0..0. .1..2..1..2. .0..1..0..0. .1..2..1..0. .0..1..2..1

Crossrefs

Row 3 of A268971.

Sequence in context: A022719 A290405 A048709 * A160223 A182668 A076394

Adjacent sequences: A268970 A268971 A268972 * A268974 A268975 A268976

Keyword

nonn

Author

R. H. Hardin, Feb 16 2016

Status

approved