
COMMENTS

Equivalently, the number of free distributive lattices on n points.
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.unisiegen.de), Feb 12 2004
From Robert FERREOL, 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)


REFERENCES

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: 121.
R. Balbes and P. Dwinger, Distributive Lattices, Univ. Missouri Press, 1974, see p. 97.  N. J. A. Sloane, Aug 15 2010
J. Berman, "Free spectra of 3element 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.
R. Church, Numerical analysis of certain free distributive lattices, Duke Math. J., 6 (1946), 732734.  N. J. A. Sloane, Aug 15 2010
L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 273.
M. A. Harrison, Introduction to Switching and Automata Theory. McGraw Hill, NY, 1965, p. 188.
W. F. Lunnon, The IU function: the size of a free distributive lattice, pp. 173181 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. M. Riviere, Recursive formulas on free distributive lattices, J. Combin. Theory, 5 (1968), 229234.  N. J. A. Sloane, Aug 15 2010
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).
D. B. West, Introduction to Graph Theory, 2nd ed., PrenticeHall, NJ, 2001, p. 349.


LINKS

Table of n, a(n) for n=0..8.
K. S. Brown, Dedekind's problem
J. Berman, Free spectra of 3element algebras, R. S. Freese and O. C. Garcia, editors, Universal Algebra and Lattice Theory (Puebla, 1982), Lect. Notes Math. Vol. 1004, 1983. (Annotated scanned copy)
Jacob North Clark, Stephen MontgomerySmith, Shapleylike values without symmetry, arXiv:1809.07747 [econ.TH], 2018.
J. L. King, Brick tiling and monotone Boolean functions
D. J. Kleitman, On Dedekind's problem: The number of monotone Boolean functions, Proc. Amer. Math. Soc. 21 1969 677682.
D. J. Kleitman and G. Markowsky, On Dedekind's problem: the number of isotone Boolean functions. II, Trans. Amer. Math. Soc. 213 (1975), 373390.
N. J. A. Sloane, My favorite integer sequences, in Sequences and their Applications (Proceedings of SETA '98).
M. Ward, Note on the order of the free distributive lattice, Bull. Amer. Math. Soc., (1946), Abstract 525135 p.423.  N. J. A. Sloane, Aug 15 2010
Eric Weisstein's World of Mathematics, Antichain
D. H. Wiedemann, A computation of the eighth Dedekind number, Order 8 (1991) 56.
K. Yamamoto, Logarithmic order of free distributive lattice, Math. Soc. Japan, 6 (1954), 343353.  N. J. A. Sloane, Aug 15 2010
Index entries for sequences related to Boolean functions
