OFFSET
4,1
FORMULA
G.f. -(1+x^2+4*x^3) + (1-x+x^3)*c(x) with the g.f. c(x):=(1-sqrt(1-4*x))/(2*x) of A000108 (Catalan).
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wolfdieter Lang, Jan 13 2006
STATUS
approved