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 A266910 #9 Jan 06 2016 12:06:52
%S A266910 1,12,210,5520,206760,10473120,688821840,57039171840,5805880778880,
%T A266910 712594633766400,103804864923513600,17709509301413529600,
%U A266910 3498328696524626764800,792308057159314683187200,203965258080479292004608000,59229266937652347633377280000,19270409372174365076286590976000
%N A266910 Number of size 2 subsets of S_n that generate a transitive subgroup of S_n.
%F A266910 a(n) = (A122949(n) - (n - 1)!)/2.
%e A266910 a(3) = 12 because there are 15 = binomial(3!,2) size 2 subsets of S_3 and every such subset generates a transitive subgroup of S_3 except: {(),(12)}, {(),(13)}, {(),(23)}.
%t A266910 nn = 20; a = Sum[n!^2 x^n/n!, {n, 0, nn}]; Drop[(Range[0, nn]! CoefficientList[Series[Log[a], {x, 0, nn}], x] - Table[(n - 1)!, {n, 0, nn}])/2, 2]
%Y A266910 Cf. A122949.
%K A266910 nonn
%O A266910 2,2
%A A266910 _Geoffrey Critzer_, Jan 05 2016