OFFSET
0,2
COMMENTS
Row sum of A158687. - Paul Barry, Mar 24 2009
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..500
Index entries for linear recurrences with constant coefficients, signature (2,2,1).
FORMULA
a(n) = Sum_{k=0..n} Sum_{j=0..n-k} C(n-j,k)*C(2k,j). - Paul Barry, Mar 24 2009
a(n) = 2*a(n-1) + 2*a(n-2) + a(n-3) with a(0) = 1, a(1) = 2, a(2) = 6. - Taras Goy, Aug 04 2017
MATHEMATICA
CoefficientList[Series[1/(1-2*x-2*x^2-x^3), {x, 0, 40}], x] (* or *) LinearRecurrence[{2, 2, 1}, {1, 2, 6}, 40] (* Vladimir Joseph Stephan Orlovsky, Jan 30 2012 *)
PROG
(PARI) Vec(1/(1-2*x-2*x^2-x^3)+O(x^99)) \\ Charles R Greathouse IV, Jan 31 2012
(Magma) I:=[1, 2, 6]; [n le 3 select I[n] else 2*Self(n-1)+2*Self(n-2)+Self(n-3): n in [1..30]]; // Vincenzo Librandi, Jul 06 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Nov 17 2002
STATUS
approved