

A166286


Number of Dyck paths with no UUU's and no DDD's, of semilength n having no peak plateaux (U=(1,1), D=(1,1)).


1



1, 1, 2, 3, 5, 9, 17, 34, 70, 147, 313, 673, 1459, 3185, 6995, 15445, 34265, 76342, 170744, 383214, 862814, 1948299, 4411167, 10011973, 22775773, 51920833, 118593423, 271376295, 622047011, 1428128025, 3283679333, 7560750299
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OFFSET

0,3


COMMENTS

A peak plateau is a run of consecutive peaks that is preceded by an upstep U and followed by a down step D; a peak consists of an upstep followed by a downstep.


LINKS

Table of n, a(n) for n=0..31.


FORMULA

a(n) = A166285(n,0).
G.f.: G(z) satisfies G = 1 + zG + z^2*G + z^3*G[G  1/(1z)].


EXAMPLE

a(3)=3 because we have UDUDUD, UDUUDD, and UUDDUD (UUDUDD is a peak plateau).


MAPLE

F := RootOf(G = 1+z*G+z^2*G+z^3*G*(G1/(1z)), G): Fser := series(F, z = 0, 35): seq(coeff(Fser, z, n), n = 0 .. 32);


CROSSREFS

Cf. A166285.
Sequence in context: A094373 A213705 A061902 * A179807 A110113 A137155
Adjacent sequences: A166283 A166284 A166285 * A166287 A166288 A166289


KEYWORD

nonn


AUTHOR

Emeric Deutsch, Oct 12 2009


STATUS

approved



