R. L. Ashenhurst, The application of counting techniques, Proc. ACM Nat. Mtg., Pittsburg, 1952, 293-305.
M. A. Harrison, The number of transitivity sets of Boolean functions, J. Soc. Indust. Appl. Math., 11 (1963), 806-828.
M. A. Harrison, Introduction to Switching and Automata Theory. McGraw Hill, NY, 1965, p. 143.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (Includes this sequence, correctly, although in the Preface on page viii 4336 is mis-typed as 4436).