OFFSET
0,6
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..1000
M. H. Albert, M. D. Atkinson and Robert Brignall, The enumeration of three pattern classes, arXiv:1206.3183 [math.CO] (2012), p. 17 (Lemma 4.6).
Index entries for linear recurrences with constant coefficients, signature (2,3,-4,-4).
FORMULA
G.f.: x^4*(1-3*x^2-x^3)/((1+x)*(1-2*x)*(1-x-2*x^2)).
a(n) = (2^(n-5)*(3*n+38)-(3*n-14)*(-1)^n)/27 with n>3, a(0)=a(1)=a(2)=a(3)=0. [Bruno Berselli, Nov 29 2012]
MATHEMATICA
CoefficientList[Series[x^4 (1 - 3 x^2 - x^3)/((1 + x) (1 - 2 x) (1 - x - 2 x^2)), {x, 0, 36}], x] (* Bruno Berselli, Nov 30 2012 *)
PROG
(Maxima) makelist(coeff(taylor(x^4*(1-3*x^2-x^3)/((1+x)*(1-2*x)*(1-x-2*x^2)), x, 0, n), x, n), n, 0, 36); /* Bruno Berselli, Nov 29 2012 */
(Magma) I:=[0, 0, 0, 0, 1, 2, 4, 9]; [n le 8 select I[n] else 2*Self(n-1) + 3*Self(n-2) - 4*Self(n-3) - 4*Self(n-4): n in [1..40]]; // Vincenzo Librandi, Dec 15 2012
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Nov 28 2012
STATUS
approved