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Search: id:A138619
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| A138619 |
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Number of permutations of length n which are contained in a pin sequence. |
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+0
1
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| 1, 2, 6, 24, 120, 664, 3596, 19004, 99596, 521420, 2731292, 14313052, 75016940, 393181820, 2060736460, 10800601788, 56607287052, 296685718140, 1554966533836, 8149773122044, 42713977098636, 223869280280316
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OFFSET
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1,2
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REFERENCES
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R. Brignall, N. Ruskuc and V. Vatter, Simple permutations: decidability and unavoidable substructures, Theoretical Computer Science, Vol. 391 (2008), oo. 150-163.
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LINKS
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F. Bassino, M. Bouvel, and D. Rossin, Enumeration of pin-permutations. [From Vince Vatter (vatter(AT)gmail.com), Sep 15 2009]
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FORMULA
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G.f.: (1-7*x+13*x^2-17*x^3+2*x^4-8*x^5+12*x^6+12*x^7-8*x^8) / (1-8*x+19*x^2-26*x^3+14*x^4-12*x^5-8*x^6+20*x^7-8*x^8) [From Vince Vatter (vatter(AT)gmail.com), Sep 15 2009]
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EXAMPLE
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a(5)=120 because all permutations of length 5 can be embedded into pin sequences.
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CROSSREFS
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Sequence in context: A152346 A152336 A152343 this_sequence A152344 A152340 A152347
Adjacent sequences: A138616 A138617 A138618 this_sequence A138620 A138621 A138622
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KEYWORD
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nonn
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AUTHOR
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Vince Vatter (vince(AT)mcs.st-and.ac.uk), May 14 2008
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EXTENSIONS
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Extending by Vince Vatter using generating function found by Bassino, Bouvel, and Rossin. Vince Vatter (vatter(AT)gmail.com), Sep 15 2009
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