%N Related to number of topologies.
%D Research Bulletin of East Panjab University, Vol. 19 (1968), p. 240 (author and title needed, also a more precise definition).
%D N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%A _N. J. A. Sloane_, Jun 11 2012