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%I #9 Dec 06 2019 21:48:53
%S 1,15,124,2431,68766,3025596,173773496,12786773247,1169623901221,
%T 130305653188890,17376934722757908,2733655198336260124,
%U 501034099176714376118,105847486572700895182728,25534322201330399433420024,6976464857439636995547805183
%N Number of subgroups of index n in fundamental group of a certain fiber space.
%D 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.
%D R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.13(c), Eq. (5.125).
%F a(n) = Sum_{m|n} A027837(m) * (n/m)^(2*m+1). - _Sean A. Irvine_, Dec 06 2019
%Y Cf. A027841, A027838, A027840.
%K nonn
%O 1,2
%A _N. J. A. Sloane_.
%E More terms from _Sean A. Irvine_, Dec 06 2019
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