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 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 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

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Last modified May 25 03:00 EDT 2013. Contains 225634 sequences.