A057013 Number of conjugacy classes of subgroups of index n in free group of rank n.

1, 3, 41, 14120, 207009649, 193466859054994, 16390021452000128467345, 173238117954686651535535048940928, 300679800156605267097630253972085058107938561

Offset: 1

Author

N. J. A. Sloane, Sep 09 2000

Keywords

• nonn

References

• R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.13(c), pp. 76, 112.

Links

• J. H. Kwak and J. Lee, Enumeration of connected graph coverings, J. Graph Th., 23 (1996), 105-109.
• 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.
• V. A. Liskovets, Reductive enumeration under mutually orthogonal group actions, Acta Applic. Math., 52 (1998), 91-120.
• Index entries for sequences related to groups

Crossrefs

Cf. A057004-A057012.

Extensions

More terms from Francisco Salinas (franciscodesalinas(AT)hotmail.com), Dec 25 2001