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A026565 a(n) = 6*a(n-2), starting 1,3,9. 2
1, 3, 9, 18, 54, 108, 324, 648, 1944, 3888, 11664, 23328, 69984, 139968, 419904, 839808, 2519424, 5038848, 15116544, 30233088, 90699264, 181398528, 544195584, 1088391168, 3265173504, 6530347008, 19591041024, 39182082048 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

a(n) = T(n,0) + T(n,1) + ... T(n,2n), T given by A026552.

LINKS

Table of n, a(n) for n=0..27.

Index entries for linear recurrences with constant coefficients, signature (0,6).

FORMULA

G.f.: (1+3*x+3x^2)/(1-6*x^2). - Ralf Stephan, Feb 03 2004

a(0)=1, a(1)=3; a(n)=3*a(n-1) if n is even, a(n)=2*a(n-1) if n is odd. [Vincenzo Librandi, Nov 19 2010]

CROSSREFS

Cf. A026532, A026534, A026551, A026567.

Sequence in context: A056372 A181574 A101652 * A174470 A190905 A133136

Adjacent sequences:  A026562 A026563 A026564 * A026566 A026567 A026568

KEYWORD

nonn,easy

AUTHOR

Clark Kimberling

EXTENSIONS

Better name from Ralf Stephan, Jul 17 2013

STATUS

approved

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Last modified September 30 12:21 EDT 2020. Contains 337439 sequences. (Running on oeis4.)