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A318943
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Number of Dyck paths with n nodes and altitude 3.
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2
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0, 0, 0, 1, 6, 21, 68, 208, 612, 1752, 4916, 13588, 37128, 100548, 270404, 723208, 1925844, 5110644, 13524872, 35713828, 94140900, 247806600, 651572660, 1711695508, 4493475336, 11789439876, 30917835908, 81053196808, 212426303892, 556607396532
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OFFSET
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0,5
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REFERENCES
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Czabarka, É., Flórez, R., Junes, L., & Ramírez, J. L. (2018). Enumerations of peaks and valleys on non-decreasing Dyck paths. Discrete Mathematics, 341(10), 2789-2807.
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LINKS
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FORMULA
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a(n) = 7*a(n-1) - 17*a(n-2) + 16*a(n-3) - 4*a(n-4) for n>7. - Colin Barker, Apr 11 2019
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MAPLE
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(1-x)^2*x^3*(1+x-3*x^2)/(1-2*x)^2/(1-3*x+x^2) ;
taylor(%, x=0, 30) ;
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PROG
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(PARI) concat([0, 0, 0], Vec(x^3*(1 - x)^2*(1 + x - 3*x^2) / ((1 - 2*x)^2*(1 - 3*x + x^2)) + O(x^40))) \\ Colin Barker, Apr 11 2019
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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