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A136659
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Unsigned third column (k=2) of triangle A136656 divided by 4.
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3
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1, 9, 75, 660, 6300, 65520, 740880, 9072000, 119750400, 1696464000, 25686460800, 414096883200, 7083236160000, 128152088064000, 2445351068160000, 49084865077248000, 1033983353475072000, 22808456326656000000
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OFFSET
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0,2
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COMMENTS
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Also unsigned second column of triangle A136657 divided by 2.
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REFERENCES
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Ch. A. Charalambides, Enumerative Combinatorics, Chapman & Hall/CRC, Boca Raton, Florida, 2002, Table 8.3, p. 311, with s=-2, k=2 column/4.
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LINKS
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Table of n, a(n) for n=0..17.
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FORMULA
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a(n)= |A136656(n+2,2)|/4, n>=0.
E.g.f.(derived from the one given for the column k=2 under A136656): (2+6*x-3*x^2)/(2*(1-x)^6).
a(n)=(n+4)!/2 * sum((k+1)!/(k+4)!,k=1..n), with offset 1 [From Gary Detlefs, Jul 27 2010]
a(n)= 1/48 * (n+8)*(n+1)*(n+3)! [From Gary Detlefs, Aug 03 2010]
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CROSSREFS
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Cf. A001710 (1/2 of unsigned k=1 column of A136657). A136660 (k=3 column divided by 8).
Sequence in context: A095249 A190983 A223204 * A126965 A066222 A080254
Adjacent sequences: A136656 A136657 A136658 * A136660 A136661 A136662
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KEYWORD
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nonn,easy
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AUTHOR
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Wolfdieter Lang Feb 22 2008
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STATUS
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approved
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