1,2

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).

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.

Main diagonal of A049290.

Sequence in context: A030262 A107173 A100494 this_sequence A167582 A068420 A128296

Adjacent sequences: A057011 A057012 A057013 this_sequence A057015 A057016 A057017

nonn

N. J. A. Sloane (njas(AT)research.att.com), Sep 09 2000

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