A016137 Expansion of 1/((1-3x)(1-6x)).

1, 9, 63, 405, 2511, 15309, 92583, 557685, 3352671, 20135709, 120873303, 725416965, 4353033231, 26119793709, 156723545223, 940355620245, 5642176768191, 33853189749309, 203119525916343, 1218718317759525

Offset

0,2

Comments

a(n) is the sum of n-th row in triangle A100852. - Reinhard Zumkeller, Nov 20 2004

Links

Table of n, a(n) for n=0..19.

Index entries for linear recurrences with constant coefficients, signature (9,-18)

Formula

a(n) = (3^n)*Stirling2(n+2, 2), n >= 0, with Stirling2(n, m) = A008277(n, m).

a(n) = -3^n + 2*6^n.

E.g.f.: (d^2/dx^2)((((exp(3*x)-1)/3)^2)/2!) = -exp(3*x) + 2*exp(6*x).

With leading zero, this is (6^n - 3^n)/3, the binomial transform of A016127 (with extra leading zero). - Paul Barry, Aug 20 2003

With leading zero, this is the fourth binomial transform of A001045, with a(n) = (2^n-1)(3^n/3 - 0^n/3) = A000225(n)*(A000244(n-1) - 0^n/3). - Paul Barry, Apr 28 2004

Sum_{k=1..n} 3^(k-1)*3^(n-k)*binomial(n, k). - Zerinvary Lajos, Sep 24 2006

a(n) = 9*a(n-1) - 18*a(n-2), n >= 2. - Vincenzo Librandi, Mar 14 2011

Mathematica

Join[{a=1, b=9}, Table[c=9*b-18*a; a=b; b=c, {n, 60}]] (* Vladimir Joseph Stephan Orlovsky, Jan 27 2011 *)
CoefficientList[Series[1/((1-3x)(1-6x)), {x, 0, 30}], x] (* or *) LinearRecurrence[{9, -18}, {1, 9}, 30] (* Harvey P. Dale, Jul 07 2012 *)

Prog

(Sage) [lucas_number1(n, 9, 18) for n in range(1, 21)] # Zerinvary Lajos, Apr 23 2009
(PARI) Vec(1/(1-3*x)/(1-6*x)+O(x^99)) \\ Charles R Greathouse IV, Sep 24 2012

Crossrefs

Second column of triangle A075498.

Cf. A017933.

Sequence in context: A316461 A022733 A111997 * A230547 A339786 A201885

Adjacent sequences: A016134 A016135 A016136 * A016138 A016139 A016140

Keyword

nonn,easy

Author

N. J. A. Sloane

Status

approved