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A137480
a(n)=4a(n-2).
1
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
0,1
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
MATHEMATICA
LinearRecurrence[{0, 4}, {12, 21}, 50] (* G. C. Greubel, Feb 23 2017 *)
PROG
(PARI) x='x + O('x^50); Vec((21*x + 12)/(-4*x^2 + 1)) \\ G. C. Greubel, Feb 23 2017
CROSSREFS
Sequence in context: A219542 A354984 A367357 * A316267 A228766 A157157
KEYWORD
nonn,easy
AUTHOR
Paul Curtz, Apr 22 2008
STATUS
approved