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%I #11 Aug 10 2019 11:12:12
%S 1,3,41,14120,207009649,193466859054994,16390021452000128467345,
%T 173238117954686651535535048940928,
%U 300679800156605267097630253972085058107938561
%N Number of conjugacy classes of subgroups of index n in free group of rank n.
%D R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.13(c), pp. 76, 112.
%H J. H. Kwak and J. Lee, <a href="http://dx.doi.org/10.1002/(SICI)1097-0118(199610)23:2%3C105::AID-JGT1%3E3.0.CO;2-X">Enumeration of connected graph coverings</a>, J. Graph Th., 23 (1996), 105-109.
%H J. H. Kwak and J. Lee, <a href="https://web.archive.org/web/20061002144237/http://com2mac.postech.ac.kr/Lecture/Lec-1.pdf">Enumeration of graph coverings and surface branched coverings</a>, Lecture Note Series 1 (2001), Com^2MaC-KOSEF, Korea. See chapter 3.
%H V. A. Liskovets, <a href="https://doi.org/10.1023/A:1005950823566">Reductive enumeration under mutually orthogonal group actions</a>, Acta Applic. Math., 52 (1998), 91-120.
%H <a href="/index/Gre#groups">Index entries for sequences related to groups</a>
%Y Cf. A057004-A057012.
%K nonn
%O 1,2
%A _N. J. A. Sloane_, Sep 09 2000
%E More terms from Francisco Salinas (franciscodesalinas(AT)hotmail.com), Dec 25 2001
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