A057007 Number of conjugacy classes of subgroups of index n in free group of rank 4.

1, 15, 235, 14120, 1712845, 371515454, 127635996839, 65417303558808, 47718183491375681, 47736450176936606373, 63553335359217380046467, 109839393591932655104274298, 241347279732331127743077516005

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

• Vaclav Kotesovec, Table of n, a(n) for n = 1..60
• 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.
• P. Vrana, On the algebra of local unitary invariants of pure and mixed quantum states, J. Phys A: Math. Theor. 44 (2011) 225304 doi:10.1088/1751-8113/44/22/225304, Table 2.

Crossrefs

Cf. A057004-A057013. Inverse Euler transform of A160446.

Extensions

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