login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A247470 Number of weak peaks in all weighted lattice paths in B(n). 1
0, 0, 0, 1, 4, 14, 43, 123, 337, 898, 2349, 6072, 15577, 39776, 101304, 257689, 655279, 1666772, 4242354, 10807191, 27557720, 70342486, 179736541, 459714008, 1176937542, 3015862454, 7734617111, 19852352861, 50992757233, 131071123062, 337122433947, 867624835207, 2234205069696 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

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.

A weak peak in a lattice path is a vertex on the top of a hump. A hump is an upstep followed by 0 or more flatsteps followed by a downstep. For example, the weighted lattice path Hu*duu*h*H*dd has 4 weak peaks (shown by the stars).

a(n) = Sum(k*A247469(n,k), k>=0).

LINKS

Table of n, a(n) for n=0..32.

M. Bona and A. Knopfmacher, On the probability that certain compositions have the same number of parts, Ann. Comb., 14 (2010), 291-306.

FORMULA

G.f. G = z^3*g/((1 - z - z^2)^2*(1 - z - z^2 - 2*z^3*g)), where g = 1 + z*g + z^2*g + z^3*g^2.

EXAMPLE

a(4) = 4  because B(4) = {hhhh, hhH, hHh, Hhh, HH, hu*d, u*h*d, u*dh} (weak peaks shown by *).

MAPLE

G := z^3*g/((1-z-z^2)^2*(1-z-z^2-2*z^3*g)): eq := g = 1+z*g+z^2*g+z^3*g^2: g := RootOf(eq, g): Gser := series(G, z = 0, 35): seq(coeff(Gser, z, n), n = 0 .. 32);

CROSSREFS

Cf. A247469

Sequence in context: A135483 A095377 A296253 * A049539 A037528 A292718

Adjacent sequences:  A247467 A247468 A247469 * A247471 A247472 A247473

KEYWORD

nonn

AUTHOR

Emeric Deutsch, Sep 17 2014

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified July 15 14:07 EDT 2019. Contains 325030 sequences. (Running on oeis4.)