login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A027841 Number of subgroups of index n in fundamental group of a certain fiber space. 3
1, 31, 301, 6491, 151711, 6673555, 362072313, 26375525171, 2384038557346, 264381564291841, 35133143655949285, 5515729547285229215, 1009373492449379396535, 212997911098253654157543, 51337590023914004777654131, 14016616814681248497416279139 (list; graph; refs; listen; history; text; internal format)
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: A327561 A279980 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 26 23:01 EDT 2020. Contains 338033 sequences. (Running on oeis4.)