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A057012 Number of conjugacy classes of subgroups of index 6 in free group of rank n. 2
1, 624, 504243, 371515454, 268530771271, 193466859054994, 139311082645798043, 100305771690618678654, 72220370631411094037391, 51998692654400641678907114, 37439061807069469917891862243 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
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.
PROG
(PARI) a(n)=if(n<0, 0, n--; 720^n-120^n+24^n+18^n-16^n+12^n*2-36^n/2-9^n/2+8^n*2/3-6^n/2-4^n*3/2-3^n/2+2^n*5/6)
CROSSREFS
Sequence in context: A006912 A318939 A223215 * A115484 A005081 A210115
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 March 28 07:48 EDT 2024. Contains 371235 sequences. (Running on oeis4.)