

A247298


Number of weighted lattice paths B(n) having no uudd strings.


1



1, 1, 2, 4, 8, 17, 36, 80, 180, 410, 946, 2203, 5173, 12233, 29108, 69643, 167437, 404311, 980125, 2384441, 5819576, 14245384, 34964611, 86032272, 212172668, 524371704, 1298509438, 3221425567, 8005623916, 19926840746, 49674610998, 124006308008
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OFFSET

0,3


COMMENTS

B(n) is the set of lattice paths of weight n that start in (0,0), end on the horizontal axis and never go below this axis, whose steps are of the following four kinds: h = (1,0) of weight 1, H = (1,0) of weight 2, u = (1,1) of weight 2, and d = (1,1) of weight 1. The weight of a path is the sum of the weights of its steps.


LINKS



FORMULA

G.f. G = G(z) satisfies G = 1 + z*G + z^2*G + z^3*G*(G  z^3 ).


EXAMPLE

a(6)=36 because among the 37 (=A004148(7)) paths in B(6) only uudd contains uudd.


MAPLE

eq := G = 1+z*G+z^2*G+z^3*G*(Gz^3): G := RootOf(eq, G): Gser := series(G, z = 0, 37): seq(coeff(Gser, z, n), n = 0 .. 35);


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



