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 A027838 #11 Dec 06 2019 21:48:45
%S A027838 1,7,22,111,486,3772,29142,275871,2830459,32028882,392744078,
%T A027838 5201524044,73943424582,1123603726896,18176728661832,311951284854975,
%U A027838 5661698774848910,108355867352001811,2181096921557783966,46066653293892718506,1018705098450761473704
%N A027838 Number of subgroups of index n in fundamental group of a certain fiber space.
%D A027838 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 A027838 R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.13(c), Eq. (5.125).
%F A027838 a(n) = Sum_{m|n} A003319(m+1) * (n/m)^(m+1). - _Sean A. Irvine_, Dec 06 2019
%Y A027838 Cf. A027841, A027839, A027840.
%K A027838 nonn
%O A027838 1,2
%A A027838 _N. J. A. Sloane_
%E A027838 More terms from _Sean A. Irvine_, Dec 06 2019