A221756 - OEIS

The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

A221756

Number of 2 X n arrays of occupancy after each element moves to some horizontal or antidiagonal neighbor, without move-in move-out straight through or left turns.

0, 2, 1, 9, 17, 64, 171, 536, 1558, 4689, 13889, 41437, 123228, 366983, 1092232, 3251610, 9679073, 28813033, 85770153, 255320984, 760038643, 2262482568, 6734954798, 20048604913, 59680661697, 177657315701, 528850071604 (list; graph; refs; listen; history; text; internal format)

	OFFSET	`1,2`
	COMMENTS	`Row 2 of A221755.`
	LINKS	`R. H. Hardin, Table of n, a(n) for n = 1..210`
	FORMULA	`Empirical: a(n) = a(n-1) + 6a(n-2) + a(n-3) - 4a(n-4).` `Empirical g.f.: x^2(2 - x - 4x^2) / (1 - x - 6x^2 - x^3 + 4x^4). - Colin Barker, Aug 10 2018`
	EXAMPLE	`Single solution for n=3:` `..0..2..1` `..1..2..0`
	CROSSREFS	`Cf. A221755.` `Sequence in context: A214884 A083162 A178075 * A094633 A261060 A144244` `Adjacent sequences: A221753 A221754 A221755 * A221757 A221758 A221759`
	KEYWORD	`nonn`
	AUTHOR	`R. H. Hardin, Jan 24 2013`
	STATUS	`approved`

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 18 21:06 EST 2021. Contains 340262 sequences. (Running on oeis4.)