OFFSET
1,3
REFERENCES
R. K. Guy, Letter to N. J. A. Sloane, Feb 05 1986.
LINKS
Colin Barker, Table of n, a(n) for n = 1..1000
R. K. Guy, Letter to N. J. A. Sloane, Feb 1986
Index entries for linear recurrences with constant coefficients, signature (1,1,0,1).
FORMULA
G.f.: -x*(2*x^2-x+1) / (x^3-x^2+2*x-1). - Colin Barker, Jul 12 2015
MATHEMATICA
LinearRecurrence[{1, 1, 0, 1}, {1, 1, 3, 6}, 40] (* Vincenzo Librandi, Jul 12 2015 *)
PROG
(Magma) I:=[1, 1, 3, 6]; [n le 4 select I[n] else Self(n-1)+Self(n-2)+Self(n-4): n in [1..40]]; // Vincenzo Librandi, Jul 12 2015
(PARI) Vec(-x*(2*x^2-x+1)/(x^3-x^2+2*x-1) + O(x^50)) \\ Colin Barker, Jul 12 2015
(Haskell)
a259968 n = a259968_list !! n
a259968_list = 1 : 1 : 3 : 6 : zipWith3 (((+) .) . (+))
a259968_list (drop 2 a259968_list) (drop 3 a259968_list)
-- Reinhard Zumkeller, Jul 12 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Jul 11 2015
EXTENSIONS
a(28)-a(37) from Hiroaki Yamanouchi, Jul 12 2015
STATUS
approved