

A027053


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


2



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
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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 latticeanimals of globally bounded width.
Index to sequences with linear recurrences with constant coefficients, signature (2,0,0,1).


FORMULA

G.f.: x^2*(1+x)^2/((1x)*(1xx^2x^3)).
a(n) = A089068(n1)+A089068(n).
a(n) = a(n1) + a(n2) + a(n3) + 4. [From David Bevan, Sep 09 2009]
a(n) = A001590(n+3)  2. [From David Bevan, Sep 09 2009]
a(n+1)a(n) = A000213(n+1).  R. J. Mathar, Aug 04 2013


CROSSREFS

Sequence in context: A019454 A019453 A038089 * A122039 A083706 A229072
Adjacent sequences: A027050 A027051 A027052 * A027054 A027055 A027056


KEYWORD

nonn


AUTHOR

Clark Kimberling


STATUS

approved



