A027841 Number of subgroups of index n in fundamental group of a certain fiber space.

1, 31, 301, 6491, 151711, 6673555, 362072313, 26375525171, 2384038557346, 264381564291841, 35133143655949285, 5515729547285229215, 1009373492449379396535, 212997911098253654157543, 51337590023914004777654131, 14016616814681248497416279139

Offset

1,2

Links

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

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.

Formula

a(n) = Sum_{m|n} A027840(m) * (n/m)^(2*m+2). - Sean A. Irvine, Dec 07 2019

Crossrefs

Cf. A027838, A027839, A027840.

Sequence in context: A279980 A369173 A001298 * A221853 A000500 A141912

Adjacent sequences: A027838 A027839 A027840 * A027842 A027843 A027844

Keyword

nonn

Author

N. J. A. Sloane.

Extensions

More terms from Sean A. Irvine, Dec 07 2019

Status

approved