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Search: id:A057011
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| A057011 |
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Number of conjugacy classes of subgroups of index 5 in free group of rank n. |
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+0
1
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| 1, 97, 13753, 1712845, 207009649, 24875000437, 2985789977353, 358313458071085, 42998059096839649, 5159777705044971877, 619173578774772949753, 74300835546376264277725
(list; graph; listen)
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OFFSET
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1,2
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REFERENCES
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J. H. Kwak and J. Lee, J. Graph Th., 23 (1996), 105-109.
V. A. Liskovets, Reductive enumeration under mutually orthogonal group actions, Acta Applic. Math., 52 (1998), 91-120.
R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.13(c), pp. 76, 112.
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LINKS
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J. H. Kwak and J. Lee, Enumeration of graph coverings and surface branched coverings, Lecture Note Series 1 (2001), Com^2MaC-KOSEF, Korea. See chapter 3.
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FORMULA
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G.f.: x(1-76x+4336x^2-81504x^3+522720x^4-1064448x^5)/((1-2x)(1-4x)(1-5x)(1-6x)(1-12x)(1-24x)(1-120x)). a(n)=120^(n-1)-24^(n-1)-12^(n-1)+6^(n-1)+5^(n-1)+4^(n-1)-2^(n-1).
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PROGRAM
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(PARI) a(n)=if(n<0, 0, n--; 120^n-24^n-12^n+6^n+5^n+4^n-2^n)
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CROSSREFS
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Cf. A057004-A057013.
Sequence in context: A017813 A017760 A069419 this_sequence A122128 A114430 A033418
Adjacent sequences: A057008 A057009 A057010 this_sequence A057012 A057013 A057014
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KEYWORD
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nonn
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AUTHOR
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njas, Sep 09 2000
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EXTENSIONS
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More terms from Francisco Salinas (franciscodesalinas(AT)hotmail.com), Dec 25 2001
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