OFFSET
0,2
COMMENTS
Third column of A107661.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (3,3,-9).
FORMULA
G.f.: (1+3*x)/((1-3*x)*(1-3*x^2)).
a(2n) = 3^(2n+1) - 2*3^n; a(2n+1) = 9^(n+1) - 3^(n+1).
MATHEMATICA
CoefficientList[Series[(1 + 3 x) / ((1 - 3 x) (1 - 3 x^2)), {x, 0, 40}], x] (* Vincenzo Librandi, Aug 17 2013 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved