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 A247288 Triangle read by rows: T(n,k) is the number of peakless Motzkin paths of length n having k weak peaks. 2
 1, 1, 1, 0, 1, 0, 1, 1, 0, 2, 1, 1, 0, 4, 2, 1, 1, 0, 8, 4, 3, 1, 1, 0, 16, 8, 7, 4, 1, 1, 0, 32, 16, 17, 10, 5, 1, 1, 0, 64, 32, 41, 26, 14, 6, 1, 1, 0, 128, 64, 98, 66, 39, 19, 7, 1, 1, 0, 256, 128, 232, 164, 107, 56, 25, 8, 1, 1, 0, 512, 256, 544, 400, 286, 164, 78, 32, 9, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,10 COMMENTS A weak peak of a Motzkin 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 peakless Motzkin path uhu*h*ddu*h*h*d where u=(1,1), h=(1,0), d(1,-1), has 5 weak peaks (shown by the stars). Row n (n>=1) contains n entries. Sum of entries in row n is the RNA secondary structure number A004148(n). Sum(k*T(n,k), 0<=k<=n) = A247289(n). LINKS Alois P. Heinz, Rows n = 0..141, flattened FORMULA The g.f. G(t,z) satisfies G = 1 + z*G + z^2*(G - 1 - z/(1-z) + t^2*z/(1-t*z))*G. EXAMPLE Row 4 is 1,0,2,1 because the peakless Motzkin paths hhhh, u*h*dhh, hu*h*dh, and u*h*h*d  have 0, 2, 2, and 3 weak peaks (shown by the stars). Triangle starts: 1; 1; 1,0; 1,0,1; 1,0,2,1; 1,0,4,2,1; 1,0,8,4,3,1; MAPLE eq := G = 1+z*G+z^2*(G-1-z/(1-z)+t^2*z/(1-t*z))*G: G := RootOf(eq, G): Gser := simplify(series(G, z = 0, 16)): for n from 0 to 14 do P[n] := sort(expand(coeff(Gser, z, n))) end do: 1; for n to 14 do seq(coeff(P[n], t, k), k = 0 .. n-1) end do; # yields sequence in triangular form CROSSREFS Cf. A004148, A247289. Sequence in context: A324642 A326757 A147787 * A135221 A318686 A214546 Adjacent sequences:  A247285 A247286 A247287 * A247289 A247290 A247291 KEYWORD nonn,tabf AUTHOR Emeric Deutsch, Sep 14 2014 STATUS approved

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Last modified September 28 09:32 EDT 2021. Contains 347714 sequences. (Running on oeis4.)