A099139 a(n) = (18^n - (-6)^n)/24.

0, 1, 12, 252, 4320, 79056, 1415232, 25520832, 459095040, 8265390336, 148766948352, 2677865536512, 48201216860160, 867624080265216, 15617220384079872, 281110045277601792, 5059980344811847680, 91079649027723165696, 1639433665572357537792, 29509806081862392348672

Offset: 0

Author

Paul Barry, Sep 29 2004

Keywords

• easy
• nonn

Comments

In general k^(n-1)*A015518(n) is given by ((3k)^n-(-k)^n)/(4k) with g.f. x/((1+kx)(1-3kx)).

Links

• Index entries for linear recurrences with constant coefficients, signature (12,108).

Crossrefs

Cf. A053524, A053535, A053536, A053537.

Programs

Mathematica

LinearRecurrence[{12,108},{0,1},20] (* Harvey P. Dale, May 24 2015 *)

Formula

G.f.: x/((1+6x)*(1-18x)).

a(n) = 12a(n-1)+108a(n-2). a(n) = 6^(n-1)*A015518(n).