A027840 Number of subgroups of index n in fundamental group of a certain fiber space.

1, 15, 220, 5275, 151086, 6605004, 362069912, 26370058035, 2384037107365, 264380945199210, 35133143655934644, 5515729438742221708, 1009373492449379367974, 212997911074525038601560, 51337590023913924398371080, 14016616814674335739387516003

Offset

1,2

Links

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

Sean A. Irvine, Java program (github).

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.

Crossrefs

Cf. A027838, A027839, A027841, A060240.

Sequence in context: A238538 A289160 A027843 * A279530 A057500 A137916

Adjacent sequences: A027837 A027838 A027839 * A027841 A027842 A027843

Keyword

nonn

Author

N. J. A. Sloane.

Extensions

Third term corrected from 240 to 220, Aug 15 1999

More terms from Sean A. Irvine, Dec 07 2019

Status

approved