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Search: id:A057004
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| A057004 |
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Array T(n,k) = number of conjugacy classes of subgroups of index k in free group of rank n, read by antidiagonals. |
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10
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| 1, 1, 1, 1, 3, 1, 1, 7, 7, 1, 1, 15, 41, 26, 1, 1, 31, 235, 604, 97, 1, 1, 63, 1361, 14120, 13753, 624, 1, 1, 127, 7987, 334576, 1712845, 504243, 4163, 1, 1, 255, 47321, 7987616, 207009649, 371515454, 24824785, 34470, 1, 1, 511, 281995, 191318464
(list; table; graph; listen)
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OFFSET
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1,5
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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.
M. Hofmeister, A Note on Counting Connected Graph Covering Projections, SIAM J. Discrete Math., 11 (1998), 286-292. See page 291 Table 4.3.
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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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EXAMPLE
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Array T(n,k) begins:
1 1 1 1 1 1 1 ...
1 3 7 26 97 624 4163 ...
1 7 41 604 13753 504243 ...
1 15 235 14120 1712845 ...
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CROSSREFS
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Rows, columns, main diagonal give A057005-A057013.
Sequence in context: A046802 A022166 A058669 this_sequence A059328 A075440 A137470
Adjacent sequences: A057001 A057002 A057003 this_sequence A057005 A057006 A057007
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KEYWORD
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nonn,tabl,nice
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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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