A109774 a(n) = (3^(n-1) - 1) * (3^n - 1)/2.

0, 8, 104, 1040, 9680, 88088, 795704, 7170080, 64556960, 581091368, 5230058504, 47071235120, 423643241840, 3812795553848, 34315179116504, 308836669444160, 2779530197184320, 25015772291219528, 225141952170657704, 2026277574184965200, 18236498181611824400

Offset

1,2

Links

Table of n, a(n) for n=1..21.

Index entries for linear recurrences with constant coefficients, signature (13,-39,27).

Formula

From R. J. Mathar, Nov 07 2015: (Start)

G.f.: -8*x^2/((x - 1)*(3*x - 1)*(9*x - 1)).

a(n) = 8*A006100(n). (End)

E.g.f.: exp(x)*(3 - 4*exp(2*x) + exp(8*x))/6. - Stefano Spezia, Apr 03 2023

Maple

A109774:=n->(3^(n-1) - 1) * (3^n - 1)/2: seq(A109774(n), n=1..30); # Wesley Ivan Hurt, Jan 24 2017

Crossrefs

Cf. A006100.

Sequence in context: A366653 A164760 A335608 * A001657 A282185 A354064

Adjacent sequences: A109771 A109772 A109773 * A109775 A109776 A109777

Keyword

nonn,easy

Author

R. K. Guy, Aug 14 2005

Extensions

a(21) from Stefano Spezia, Apr 03 2023

Status

approved