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A057007
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Number of conjugacy classes of subgroups of index n in free group of rank 4.
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0
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1, 15, 235, 14120, 1712845, 371515454, 127635996839, 65417303558808, 47718183491375681, 47736450176936606373, 63553335359217380046467, 109839393591932655104274298, 241347279732331127743077516005
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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REFERENCES
| 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
| 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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CROSSREFS
| Cf. A057004-A057013.
Sequence in context: A097185 A178299 A097582 * A093745 A071811 A157456
Adjacent sequences: A057004 A057005 A057006 * A057008 A057009 A057010
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Sep 09 2000
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EXTENSIONS
| More terms from Francisco Salinas (franciscodesalinas(AT)hotmail.com), Dec 25 2001
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