OFFSET
0,2
COMMENTS
Odd coefficients are zero.
LINKS
Fung Lam, Table of n, a(n) for n = 0..1500
E. Barcucci, E. Pergola, R. Pinzani and S. Rinaldi, ECO method and hill-free generalized Motzkin paths, Séminaire Lotharingien de Combinatoire, B46b (2001), 14 pp.
FORMULA
G.f.: Sum[n>=0, a(n)x^(2n)] = [1-x^4+2x^2-sqrt(1-2x^4+x^8-4x^2)]/[2x^2*(2+x^2-x^4)].
Recurrence: 2*(n+10)*a(n) = (n-2)*a(n-6) + (2-n)*a(n-5) - 4*(n+1)*a(n-4) - 2*(n+10)*a(n-3) + 9*(n+6)*a(n-2) + (7*n+46)*a(n-1), where n >= 6 and is even. - Fung Lam, Feb 03 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Ralf Stephan, Oct 09 2004
STATUS
approved