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Search: id:A057012
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| A057012 |
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Number of conjugacy classes of subgroups of index 6 in free group of rank n. |
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+0
2
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| 1, 624, 504243, 371515454, 268530771271, 193466859054994, 139311082645798043, 100305771690618678654, 72220370631411094037391, 51998692654400641678907114, 37439061807069469917891862243
(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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PROGRAM
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(PARI) a(n)=if(n<0, 0, n--; 720^n-120^n+24^n+18^n-16^n+12^n*2-36^n/2-9^n/2+8^n*2/3-6^n/2-4^n*3/2-3^n/2+2^n*5\ /6)
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CROSSREFS
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Cf. A057004-A057013.
Sequence in context: A043368 A158374 A006912 this_sequence A115484 A005081 A043352
Adjacent sequences: A057009 A057010 A057011 this_sequence A057013 A057014 A057015
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), 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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