OFFSET
0,2
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..2000 (first 500 terms from R. H. Hardin)
Index entries for linear recurrences with constant coefficients, signature (2,-1,1,-1).
FORMULA
G.f.: (x+1)*(x^2+1)*(x^2-x+1)/((x-1)*(x^3+x-1)). - R. J. Mathar, Jan 19 2011
a(n) = a(n-1) + a(n-3) + 4 for n>4. - Greg Dresden, Feb 09 2020
MATHEMATICA
LinearRecurrence[{2, -1, 1, -1}, {1, 2, 4, 8, 13, 21}, 41] (* Harvey P. Dale, Sep 02 2017; amended for offset 0 by Georg Fischer, Apr 02 2019 *)
PROG
(PARI) x='x+O('x^50); Vec((x+1)*(x^2+1)*(x^2-x+1)/((x-1)*(x^3+x-1))) \\ Georg Fischer, Apr 02 2019
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
R. H. Hardin, Aug 14 2009
EXTENSIONS
Edited by Alois P. Heinz, Oct 11 2017
STATUS
approved