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 A245731 #11 May 02 2021 17:23:18
%S A245731 1,2,9,109,2647,110481,7291543,726434549,106312974249,22465350835849,
%T A245731 6771847676632679,2883916106465622053,1720792953946798909927,
%U A245731 1427968172285571102335605,1637002867699829205840095585,2577011453377960519672777065693,5541005747990556022043234479371823,16195114271558690956785525865003941945,64068293759315414337050896928055465961863
%N A245731 Number of connected labeled transitive relations on an n-set.
%F A245731 E.g.f.: log(A(x + exp(x) - 1)) + 1 where A(x) is the e.g.f. for A001035.
%e A245731 a(2) = 9. There are 13 transitive relations on the set {1,2}. Four of these are not connected: {}, {(1,1)}, {(2,2)}, {(1,1),(2,2)}. 13-4=9.
%Y A245731 Cf. A001035, A006905.
%K A245731 nonn
%O A245731 0,2
%A A245731 _Geoffrey Critzer_, Jul 30 2014