A247289 Number of weak peaks in all peakless Motzkin paths of length n.
0, 0, 0, 2, 7, 18, 45, 110, 267, 652, 1602, 3960, 9845, 24594, 61689, 155270, 391962, 991968, 2515964, 6393610, 16275174, 41491776, 105922244, 270734244, 692756227, 1774418286, 4549173861, 11672860634, 29975156134, 77029918152, 198083586300, 509692521982
Offset: 0
Keywords
Examples
a(4)=7 because the peakless Motzkin paths u*h*dhh, hu*h*dh, and u*h*h*d have 0, 2, 2, and 3 weak peaks (shown by the stars).
Links
- Alois P. Heinz, Table of n, a(n) for n = 0..1000
Programs
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Maple
f := (2-z)*z^3*g/((1-z)^2*(1-z+z^2-2*z^2*g)): eqg := g = 1+z*g+z^2*g*(g-1): g := RootOf(eqg, g): fser := series(f, z = 0, 35): seq(coeff(fser, z, n), n = 0 .. 33);
Formula
G.f.: (2-z)*z^3*g/((1-z)^2*(1-z+z^2-2*z^2*g)), where g is defined by g = 1 + z*g + z^2*g*(g-1).
D-finite with recurrence n*(n-1)*a(n) +(-7*n^2+28*n-31)*a(n-1) +(n-2)*(13*n-48)*a(n-2) +(-5*n^2+21*n-6)*a(n-3) +(7*n^2-43*n+82)*a(n-4) -(13*n-24)*(n-5)*a(n-5) +(4*n-5)*(n-6)*a(n-6)=0. - R. J. Mathar, Jul 24 2022
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