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 A027839 Number of subgroups of index n in fundamental group of a certain fiber space. 4
 1, 15, 124, 2431, 68766, 3025596, 173773496, 12786773247, 1169623901221, 130305653188890, 17376934722757908, 2733655198336260124, 501034099176714376118, 105847486572700895182728, 25534322201330399433420024, 6976464857439636995547805183 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 REFERENCES 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(c), Eq. (5.125). LINKS FORMULA a(n) = Sum_{m|n} A027837(m) * (n/m)^(2*m+1). - Sean A. Irvine, Dec 06 2019 CROSSREFS Cf. A027841, A027838, A027840. Sequence in context: A038743 A181377 A264046 * A034271 A171220 A071080 Adjacent sequences:  A027836 A027837 A027838 * A027840 A027841 A027842 KEYWORD nonn,changed AUTHOR EXTENSIONS More terms from Sean A. Irvine, Dec 06 2019 STATUS approved

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Last modified December 12 15:11 EST 2019. Contains 329960 sequences. (Running on oeis4.)