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
Links
- Index entries for linear recurrences with constant coefficients, signature (13,-39,27).
Crossrefs
Cf. A006100.
Programs
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Maple
A109774:=n->(3^(n-1) - 1) * (3^n - 1)/2: seq(A109774(n), n=1..30); # Wesley Ivan Hurt, Jan 24 2017
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
Extensions
a(21) from Stefano Spezia, Apr 03 2023