A137480 a(n)=4a(n-2).

12, 21, 48, 84, 192, 336, 768, 1344, 3072, 5376, 12288, 21504, 49152, 86016, 196608, 344064, 786432, 1376256, 3145728, 5505024, 12582912, 22020096, 50331648, 88080384, 201326592, 352321536, 805306368, 1409286144, 3221225472, 5637144576, 12884901888

Offset: 0

Author

Paul Curtz, Apr 22 2008

Keywords

• nonn
• easy

Links

• G. C. Greubel, Table of n, a(n) for n = 0..1000
• Index entries for linear recurrences with constant coefficients, signature (0,4).

Programs

Mathematica

LinearRecurrence[{0, 4}, {12, 21}, 50] (* G. C. Greubel, Feb 23 2017 *)

PARI

x='x + O('x^50); Vec((21*x + 12)/(-4*x^2 + 1)) \\ G. C. Greubel, Feb 23 2017

Formula

G.f.: (21*x + 12)/(-4*x^2 + 1).

a(n) = -(9/4)*sqrt(2)*(1/2)^(-1/2*(-1)^n)*(-2)^n + (33/4)*2^n*sqrt(2)*(1/2)^(-(1/2)*(-1)^n) - Alexander R. Povolotsky, Apr 25 2008

a(n) = 3*A133600(n+2) - R. J. Mathar, Jun 08 2016