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A026121 3^n*(3^n-1)/2. 5
0, 3, 36, 351, 3240, 29403, 265356, 2390391, 21520080, 193700403, 1743362676, 15690441231, 141214502520, 1270932117003, 11438393835996, 102945558872871, 926510072902560, 8338590785263203, 75047317454789316, 675425858255365311 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..200

Index entries for linear recurrences with constant coefficients, signature (12,-27).

FORMULA

a(n) = C(3^n,2), n>=0. - Zerinvary Lajos, Jan 07 2008

a(0) = 0, a(1)=3, a(n)=12*a(n-1)-27*a(n-2). - Harvey P. Dale, Oct 07 2012

G.f.: 3*x / ( (9*x-1)*(3*x-1) ). a(n) = 3*A016142(n-1). - R. J. Mathar, Mar 24 2013

MAPLE

seq(binomial(3^n, 2), n=0..19); # Zerinvary Lajos, Jan 07 2008

MATHEMATICA

Binomial[3^Range[0, 20], 2] (* or *) LinearRecurrence[{12, -27}, {0, 3}, 30] (* Harvey P. Dale, Oct 07 2012 *)

PROG

(MAGMA) [3^n*(3^n-1)/2: n in [0..30]]; // Vincenzo Librandi, May 01 2011

(PARI) a(n)=binomial(3^n, 2) \\ Charles R Greathouse IV, Jun 11 2015

CROSSREFS

Sequence in context: A038146 A067444 A092648 * A055303 A274403 A068177

Adjacent sequences:  A026118 A026119 A026120 * A026122 A026123 A026124

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified October 20 08:05 EDT 2019. Contains 328252 sequences. (Running on oeis4.)