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A135139
a(n) = 5*a(n-2) + 2*a(n-3).
2
1, 2, 4, 12, 24, 68, 144, 388, 856, 2228, 5056, 12852, 29736, 74372, 174384, 431332, 1020664, 2505428, 5965984, 14568468, 34840776, 84774308, 203340816, 493553092, 1186252696, 2874447092, 6918369664, 16744740852, 40340742504, 97560443588
OFFSET
0,2
FORMULA
From R. J. Mathar, Feb 15 2008: (Start)
O.g.f.: 4*(x-2)/(7*(x^2+2*x-1)) - 1/(7*(1+2*x)).
a(n) = (4*A078343(n+1)-(-2)^n)/7.
a(n) = A135138(n+2) + 2*A135138(n+1) - A135138(n). (End)
MATHEMATICA
a = {1, 2, 4}; Do[AppendTo[a, 5*a[[ -2]] + 2*a[[ -3]]], {40}]; a (* Stefan Steinerberger, Feb 15 2008 *)
LinearRecurrence[{0, 5, 2}, {1, 2, 4}, 30] (* Harvey P. Dale, May 25 2012 *)
CROSSREFS
Cf. A135138.
Sequence in context: A331392 A100538 A303794 * A161894 A062177 A348642
KEYWORD
nonn,easy
AUTHOR
Paul Curtz, Feb 13 2008
EXTENSIONS
More terms from R. J. Mathar and Stefan Steinerberger, Feb 15 2008
STATUS
approved

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