OFFSET
0,1
LINKS
Clark Kimberling, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (6, -3, -18, -9)
FORMULA
G.f.: -(((1 + x) (-2 + 3 x + 3 x^2))/(-1 + 3 x + 3 x^2)^2).
a(n) = 6*a(n-1) - 3*a(n-2) - 18*a(n-3) - 9*a(n-4) for n >= 5.
MATHEMATICA
z = 60; s = x + x^2; p = (1 - 3 s)^2;
Drop[CoefficientList[Series[s, {x, 0, z}], x], 1] (* A019590 *)
u = Drop[CoefficientList[Series[1/p, {x, 0, z}], x], 1] (* A099432 *)
u / 3 (* A291386 *)
LinearRecurrence[{6, -3, -18, -9}, {2, 11, 54, 252}, 30] (* Harvey P. Dale, Oct 06 2017 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Sep 04 2017
STATUS
approved