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A057014 Number of subgroups of index n in free group of rank n. 1
1, 3, 97, 54335, 1035045121, 1160799620549247, 114730150164000898447873, 1385904943637483363530115691960319, 2706118201409447403878672281480056877837885441 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

P. de la Harpe, Topics in Geometric Group Theory, Univ. Chicago Press, 2000, p. 23.

V. A. Liskovets and A. Mednykh, Enumeration of subgroups in the fundamental groups of orientable circle bundles over surfaces, Commun. in Algebra, 28, No. 4 (2000), 1717-1738.

R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.13(b).

LINKS

Table of n, a(n) for n=1..9.

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.

CROSSREFS

Main diagonal of A049290.

Sequence in context: A209554 A243155 A201843 * A167582 A068420 A180350

Adjacent sequences:  A057011 A057012 A057013 * A057015 A057016 A057017

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Sep 09 2000

EXTENSIONS

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

STATUS

approved

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Last modified July 31 05:43 EDT 2014. Contains 245082 sequences.