A027053 - OEIS

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A027053

T(n,n+2), T given by A027052.

1, 4, 9, 18, 35, 66, 123, 228, 421, 776, 1429, 2630, 4839, 8902, 16375, 30120, 55401, 101900, 187425, 344730, 634059, 1166218, 2145011, 3945292, 7256525, 13346832, 24548653, 45152014, 83047503, 152748174, 280947695, 516743376 (list; graph; refs; listen; history; text; internal format)

	OFFSET	`2,2`
	COMMENTS	`Second differences of (A027026(n)-1)/2.` `Pairwise sums of A089068.` `a(n) is also the number of fixed polyominoes with n cells of height (or width) 2. [From David Bevan, Sep 09 2009]`
	LINKS	`Table of n, a(n) for n=2..33.` `Doron Zeilberger, The generating functions and series expansions for 2D lattice-animals of globally bounded width.`
	FORMULA	`G.f.: [x^2(1+x)^2]/[(1-x)(1-x-x^2-x^3)].` `a(n) = a(n-1) + a(n-2) + a(n-3) + 4. [From David Bevan, Sep 09 2009]` `a(n) = A001590(n+3) - 2. [From David Bevan, Sep 09 2009]`
	CROSSREFS	`Sequence in context: A019454 A019453 A038089 * A122039 A083706 A074896` `Adjacent sequences: A027050 A027051 A027052 * A027054 A027055 A027056`
	KEYWORD	`nonn`
	AUTHOR	`Clark Kimberling`
	STATUS	`approved`

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Last modified May 19 07:18 EDT 2013. Contains 225429 sequences.