A020724 G.f.: 1/((1-6*x)*(1-9*x)*(1-12*x)).

1, 27, 495, 7695, 109431, 1474767, 19198215, 244167615, 3055792311, 37811613807, 464078786535, 5662363023135, 68791291322391, 833094971965647, 10065613312624455, 121404092777808255, 1462402531680439671

Offset

0,2

Links

Harvey P. Dale, Table of n, a(n) for n = 0..925

Index entries for linear recurrences with constant coefficients, signature (27,-234,648).

Formula

a(n) = (12^(n+2) - 2*9^(n+2) + 6^(n+2))/18. - Yahia Kahloune, Jun 30 2013

a(n) = 27*a(n-1) - 234*a(n-2) + 648*a(n-3). - Jinyuan Wang, Mar 10 2020

Mathematica

CoefficientList[Series[1/((1-6x)(1-9x)(1-12x)), {x, 0, 20}], x] (* or *) LinearRecurrence[{27, -234, 648}, {1, 27, 495}, 20] (* Harvey P. Dale, Feb 18 2025 *)

Prog

(PARI) Vec(1/((1-6*x)*(1-9*x)*(1-12*x)) + O(x^30)) \\ Jinyuan Wang, Mar 10 2020

Crossrefs

Cf. A017933.

Sequence in context: A020726 A020969 A025956 * A021994 A020568 A021734

Adjacent sequences: A020721 A020722 A020723 * A020725 A020726 A020727

Keyword

nonn,easy

Author

N. J. A. Sloane

Status

approved