A027839 Number of subgroups of index n in fundamental group of a certain fiber space.

1, 15, 124, 2431, 68766, 3025596, 173773496, 12786773247, 1169623901221, 130305653188890, 17376934722757908, 2733655198336260124, 501034099176714376118, 105847486572700895182728, 25534322201330399433420024, 6976464857439636995547805183

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

Table of n, a(n) for n=1..16.

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: A181377 A264046 A349295 * A034271 A171220 A071080

Adjacent sequences: A027836 A027837 A027838 * A027840 A027841 A027842

Keyword

nonn

Author

N. J. A. Sloane.

Extensions

More terms from Sean A. Irvine, Dec 06 2019

Status

approved