|
| |
|
|
A057012
|
|
Number of conjugacy classes of subgroups of index 6 in free group of rank n.
|
|
1
|
|
|
|
1, 624, 504243, 371515454, 268530771271, 193466859054994, 139311082645798043, 100305771690618678654, 72220370631411094037391, 51998692654400641678907114, 37439061807069469917891862243
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,2
|
|
|
REFERENCES
|
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.
|
|
|
LINKS
|
Table of n, a(n) for n=1..11.
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.
|
|
|
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
|
Cf. A057004-A057013.
Sequence in context: A158374 A006912 A223215 * A115484 A005081 A210115
Adjacent sequences: A057009 A057010 A057011 * A057013 A057014 A057015
|
|
|
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
|
| |
|
|
