0,3

A monotone Boolean function is an increasing functions from P(S), the set of subsets of S, to {0,1}.

The count of antichains excludes the empty antichain which contains no subsets and the antichain consisting of only the empty set.

The number of continuous functions f : R^n->R with f(x_1,..,x_n) in {x_1,..,x_n}. - Jan Fricke (fricke(AT)math.uni-siegen.de), Feb 12 2004

Comment from Robert FERREOL (rf(AT)mathcurve.com), Mar 23 2009 (Start): a(n) is also the number of reduced normal conjunctive forms with n variables without negation.

For example the 18 forms for n=3 are :

a

b

c

a or b

a or c

b or c

a or b or c

a and b

a and c

b and c

a and (b or c)

b and (a or c)

c and (a or b)

(a or b) and (a or c)

(b or a) and (b or c)

(c or a) and (c or b)

a and b and c

(a or b) and (a or c) and (b or c)

(End)

I. Anderson, Combinatorics of Finite Sets. Oxford Univ. Press, 1987, p. 38.

J. L. Arocha, (1987) "Antichains in ordered sets" [ In Spanish ]. Anales del Instituto de Matematicas de la Universidad Nacional Autonoma de Mexico 27: 1-21.

J. Berman, ``Free spectra of 3-element algebras,'' in R. S. Freese and O. C. Garcia, editors, Universal Algebra and Lattice Theory (Puebla, 1982), Lect. Notes Math. Vol. 1004, 1983.

G. Birkhoff, Lattice Theory. American Mathematical Society, Colloquium Publications, Vol. 25, 3rd ed., Providence, RI, 1967, p. 63.

L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 273.

M. A. Harrison, Introduction to Switching and Automata Theory. McGraw Hill, NY, 1965, p. 188.

D. J. Kleitman, On Dedekind's problem: The number of monotone Boolean functions. Proc. Amer. Math. Soc. 21 1969 677-682.

D. J. Kleitman and G. Markowsky, On Dedekind's problem: the number of isotone Boolean functions. II. Trans. Amer. Math. Soc. 213 (1975), 373-390.

W. F. Lunnon, The IU function: the size of a free distributive lattice, pp. 173-181 of D. J. A. Welsh, editor, Combinatorial Mathematics and Its Applications. Academic Press, NY, 1971.

S. Muroga, Threshold Logic and Its Applications. Wiley, NY, 1971, p. 38 and 214.

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

D. B. West, Introduction to Graph Theory, 2nd ed., Prentice-Hall, NJ, 2001, p. 349.

D. H. Wiedemann, A computation of the eighth Dedekind number, Order 8 (1991) 5-6.

K. S. Brown, Dedekind's problem

J. L. King, Brick tiling and monotone Boolean functions

N. J. A. Sloane, My favorite integer sequences, in Sequences and their Applications (Proceedings of SETA '98).

Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.

Index entries for sequences related to Boolean functions

a(2)=4 from the antichains {{1}}, {{2}}, {{1,2}}, {{1},{2}}.

Equals A000372 - 2 and A014466 - 1.. Cf. A003182.

Sequence in context: A060841 A059837 A054759 this_sequence A156870 A145075 A058924

Adjacent sequences: A007150 A007151 A007152 this_sequence A007154 A007155 A007156

nonn,hard

N. J. A. Sloane (njas(AT)research.att.com).

Last term from D. H. Wiedemann, personal communication.

Additional comments from Michael Somos, Jun 10 2002.