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A129156
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Number of primitive Dyck factors in all skew Dyck paths of semilength n. A skew Dyck path is a path in the first quadrant which begins at the origin, ends on the x-axis, consists of steps U=(1,1) (up), D=(1,-1)(down) and L=(-1,-1)(left) so that up and left steps do not overlap. The length of the path is defined to be the number of its steps. A primitive Dyck factor is a subpath of the form UPD that starts on the x-axis, P being a Dyck path.
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2
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0, 1, 3, 10, 36, 136, 532, 2139, 8796, 36859, 156946, 677514, 2959669, 13063493, 58184838, 261230814, 1181144792, 5374078726, 24588562675, 113067256235, 522270436044, 2422244159067, 11275548912967, 52663412854571
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OFFSET
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0,3
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COMMENTS
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a(n)=Sum(k*A129154(n,k),k=0..n). a(n)=A128742(n)-A129158(n).
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LINKS
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Table of n, a(n) for n=0..23.
E. Deutsch, E. Munarini, S. Rinaldi, Skew Dyck paths, J. Stat. Plann. Infer. 140 (8) (2010) 2191-2203
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FORMULA
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G.f.=[3-3z-sqrt(1-6z+5z^2)][1-sqrt(1-4z)]/[1+z+sqrt(1-6*z+5*z^2)]^2.
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EXAMPLE
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a(2)=3 because in all skew Dyck paths of semilength 3, namely (UD)(UD), (UUDD) and UUDL, we have altogether 3 primitive Dyck factors (shown between parentheses).
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MAPLE
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G:=(3-3*z-sqrt(1-6*z+5*z^2))*(1-sqrt(1-4*z))/(1+z+sqrt(1-6*z+5*z^2))^2: Gser:=series(G, z=0, 30): seq(coeff(Gser, z, n), n=0..27);
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CROSSREFS
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Cf. A129154, A129157, A129158.
Sequence in context: A007582 A026854 A136576 * A171753 A002212 A149041
Adjacent sequences: A129153 A129154 A129155 * A129157 A129158 A129159
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KEYWORD
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nonn
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AUTHOR
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Emeric Deutsch, Apr 02 2007
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STATUS
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approved
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