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A190165 Number of peakless Motzkin paths of length n having no (1,0)-steps at levels 0,2,4,... . 2
1, 0, 0, 1, 1, 1, 2, 4, 7, 12, 22, 41, 76, 142, 268, 509, 971, 1861, 3583, 6925, 13430, 26128, 50980, 99735, 195594, 384454, 757256, 1494465, 2954715, 5851677, 11607348, 23058492, 45870685, 91371464, 182231978, 363871075, 727364502, 1455503056, 2915461721, 5845386764, 11730347948 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,7

COMMENTS

a(n) = A190164(n,0).

LINKS

Table of n, a(n) for n=0..40.

FORMULA

G.f. G=G(z) satisfies the equation z^2*(1+z^2)G^2 - (1+z^2)(1-z+z^2)G + 1-z+z^2=0.

EXAMPLE

a(6)=2 because we have uhduhd and uhhhhd, where u=(1,1), h=(1,0), d=(1,-1).

MAPLE

eq := z^2*(1+z^2)*G^2-(1+z^2)*(1-z+z^2)*G+1-z+z^2 =0: g:=RootOf(eq, G): Gser:=series(g, z=0, 46): seq(coeff(Gser, z, n), n=0..40);

CROSSREFS

Cf. A190164, A190167, A190168

Sequence in context: A000072 A268306 A018179 * A127542 A023432 A072641

Adjacent sequences:  A190162 A190163 A190164 * A190166 A190167 A190168

KEYWORD

nonn

AUTHOR

Emeric Deutsch, May 06 2011

STATUS

approved

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Last modified November 21 04:41 EST 2019. Contains 329350 sequences. (Running on oeis4.)