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Search: id:A001681
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| A001681 |
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The partition function G(n,4).
(Formerly M1481 N0584)
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+0
5
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| 1, 1, 2, 5, 15, 51, 196, 827, 3795, 18755, 99146, 556711, 3305017, 20655285, 135399720, 927973061, 6631556521, 49294051497, 380306658250, 3039453750685, 25120541332271, 214363100120051, 1885987611214092, 17085579637664715
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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Number of '12-3 and 321-4'-avoiding permutations.
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
F. L. Miksa, L. Moser and M. Wyman, Restricted partitions of finite sets, Canad. Math. Bull., 1 (1958), 87-96.
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LINKS
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David Applegate and N. J. A. Sloane, The Gift Exchange Problem (arXiv:0907.0513, 2009)
P. J. Cameron, Sequences realized by oligomorphic permutation groups, J. Integ. Seqs. Vol. 3 (2000), #00.1.5.
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 19
T. Mansour, Restricted permutations by patterns of type 2-1.
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FORMULA
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E.g.f.: exp( x + x^2/2 + x^3/6 + x^4/24 ). - Ralf Stephan, Apr 22 2004
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CROSSREFS
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Cf. A001680.
Sequence in context: A153197 A108307 A117426 this_sequence A053553 A007312 A007296
Adjacent sequences: A001678 A001679 A001680 this_sequence A001682 A001683 A001684
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KEYWORD
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nonn,easy
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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More terms from Ralf Stephan, Apr 22 2004
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