OFFSET
0,4
COMMENTS
A159914 and A228705 both satisfy the same recurrence relation, and both count (n-3)-element subsets of {1..n} having even resp. odd sum. Is there a similar subset-counting interpretation for this sequence? - M. F. Hasler, Jun 22 2018
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..1000
E. Kirkman, J. Kuzmanovich and J. J. Zhang, Invariants of (-1)-Skew Polynomial Rings under Permutation Representations, arXiv preprint arXiv:1305.3973 [math.RA], 2013. See Example 5.6.
Index entries for linear recurrences with constant coefficients, signature (4,-8,12,-14,12,-8,4,-1).
FORMULA
a(n) = (n+2)*(2*(n+1)*(n+3)+9*(1+(-1)^n)*i^(n*(n+1)))/48, where i=sqrt(-1). [Bruno Berselli, Sep 07 2013]
MATHEMATICA
CoefficientList[Series[(1 - 3 x + 5 x^2 - 3 x^3 + x^4) / ((1 - x)^4 (1 + x^2)^2), {x, 0, 50}], x] (* Vincenzo Librandi, Sep 07 2013 *)
PROG
(Magma) m:=50; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!(1-3*x+5*x^2-3*x^3+x^4)/((1-x)^4*(1+x^2)^2)); // Vincenzo Librandi, Sep 07 2013
(PARI) Vec((1-3*x+5*x^2-3*x^3+x^4)/((1-x)^4*(1+x^2)^2)+O(x^99)) \\ M. F. Hasler, Jun 22 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Sep 06 2013
STATUS
approved