A156605 a(n) = (4^n + 20)/3.

7, 8, 12, 28, 92, 348, 1372, 5468, 21852, 87388, 349532, 1398108, 5592412, 22369628, 89478492, 357913948, 1431655772, 5726623068, 22906492252, 91625968988, 366503875932, 1466015503708, 5864062014812, 23456248059228, 93824992236892, 375299968947548

Offset: 0

Author

Paul Curtz, Feb 11 2009

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..1000
• Index entries for linear recurrences with constant coefficients, signature (5, -4).

Crossrefs

Cf. A002450, A154879, A156591.

Programs

Magma

[(4^n+20)/3: n in [0..35]]; // Vincenzo Librandi, Jul 24 2011

Mathematica

(4^Range[0,40] + 20)/3 (* G. C. Greubel, Jun 25 2021 *)

Sage

[(4^n + 20)/3 for n in (0..40)] # G. C. Greubel, Jun 25 2021

Formula

a(n) = -A156591(2n+1).

a(n) = 4 + A154879(2n) = 7 + A002450(n).

a(n) = 4*a(n-1) - 20, n > 0.

G.f.: (7 - 27*x)/((1-x)*(1-4*x)). - R. J. Mathar, Feb 23 2009

E.g.f.: (1/3)*(20*exp(x) + exp(4*x)). - G. C. Greubel, Jun 25 2021

Extensions

Edited and extended by R. J. Mathar, Feb 23 2009