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 A113182 #8 Aug 30 2019 22:11:36
%S A113182 1,1,2,3,7,14,39,95,308,859,3013,9130,33300,106039,394340,1297295,
%T A113182 4878109,16428300,62232321,213388961,812825244,2827645453,10818489817,
%U A113182 38086408002,146250545528,520062618300,2003199281223,7184570776213
%N A113182 Number of unrooted two-vertex (or, dually, two-face) regular planar maps of valency n considered up to orientation-preserving homeomorphism.
%C A113182 Bisections are A112944 and A113181.
%H A113182 M. Bousquet, G. Labelle and P. Leroux, <a href="http://dx.doi.org/10.1016/S0012-365X(99)00406-9">Enumeration of planar two-face maps</a>, Discrete Math., vol. 222 (2000), 1-25.
%t A113182 a[n_] := If[OddQ[n], (1/(2n))(Sum[EulerPhi[d] Binomial[2 Floor[(n-1)/(2d)], Floor[(n-1)/(2d)]]^2, {d, Divisors[n]}] + n Binomial[n-1, (n-1)/2]), (1/4)((2 Sum[EulerPhi[d] Binomial[n/d-1, Floor[n/(2d)]]^2, {d, Divisors[ n]}])/n + Binomial[n, n/2])];
%t A113182 Array[a, 28] (* _Jean-François Alcover_, Aug 30 2019 *)
%Y A113182 Cf. A018224, A112944, A113181.
%K A113182 nonn
%O A113182 1,3
%A A113182 _Valery A. Liskovets_, Oct 19 2005