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 A027839 #11 Jul 08 2025 17:55:39
%S A027839 1,15,124,2431,68766,3025596,173773496,12786773247,1169623901221,
%T A027839 130305653188890,17376934722757908,2733655198336260124,
%U A027839 501034099176714376118,105847486572700895182728,25534322201330399433420024,6976464857439636995547805183
%N A027839 Number of subgroups of index n in fundamental group of a certain fiber space.
%D A027839 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.
%D A027839 R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.13(c), Eq. (5.125).
%F A027839 a(n) = Sum_{m|n} A027837(m) * (n/m)^(2*m+1). - _Sean A. Irvine_, Dec 06 2019
%Y A027839 Cf. A027841, A027838, A027840.
%K A027839 nonn
%O A027839 1,2
%A A027839 _N. J. A. Sloane_
%E A027839 More terms from _Sean A. Irvine_, Dec 06 2019