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A190161
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Number of subwords of type uh^ju and dh^jd (j>=1), where u=(1,1), h=(1,0), and d=(1,-1), in all peakless Motzkin paths of length n (can be easily expressed using RNA secondary structure terminology).
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1
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0, 0, 0, 0, 0, 0, 2, 10, 34, 104, 300, 834, 2270, 6094, 16206, 42818, 112606, 295138, 771616, 2013550, 5246954, 13657882, 35522364, 92331014, 239875614, 622971814, 1617463986, 4198716114, 10897812738, 28282859174, 73398069768, 190474295608, 494298218888, 1282776917922
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OFFSET
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0,7
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COMMENTS
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LINKS
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FORMULA
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G.f.: G(z)=2z^3*g^3*(g-1)/[(1-z)(1-z^2*g^2)], where g=1+zg+z^2*g(g-1).
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EXAMPLE
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a(6)=2 because among the 17 (=A004148(6)) peakless Motzkin paths of length 6 only (uhu)hdd and uuh(dhd) have subwords of the prescribed type (shown between parentheses).
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MAPLE
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eq := g = 1+z*g+z^2*g*(g-1): g := RootOf(eq, g): gser := series(2*z^5*g^3*(g-1)/((1-z)*(1-z^2*g^2)), z = 0, 38): seq(coeff(gser, z, n), n = 0 .. 33);
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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