This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A027841 #14 Jul 08 2025 17:55:55
%S A027841 1,31,301,6491,151711,6673555,362072313,26375525171,2384038557346,
%T A027841 264381564291841,35133143655949285,5515729547285229215,
%U A027841 1009373492449379396535,212997911098253654157543,51337590023914004777654131,14016616814681248497416279139
%N A027841 Number of subgroups of index n in fundamental group of a certain fiber space.
%H A027841 V. A. Liskovets and A. Mednykh, <a href="https://doi.org/10.1080/00927870008826924">Enumeration of subgroups in the fundamental groups of orientable circle bundles over surfaces</a>, Commun. in Algebra, 28, No. 4 (2000), 1717-1738.
%F A027841 a(n) = Sum_{m|n} A027840(m) * (n/m)^(2*m+2). - _Sean A. Irvine_, Dec 07 2019
%Y A027841 Cf. A027838, A027839, A027840.
%K A027841 nonn
%O A027841 1,2
%A A027841 _N. J. A. Sloane_
%E A027841 More terms from _Sean A. Irvine_, Dec 07 2019