

A133983


Number of nonisomorphic nelement selfdual posets (or partially ordered sets).


1




OFFSET

1,2


COMMENTS

Posets whose Hasse diagram looks the same if it is turned upside down.  N. J. A. Sloane, Mar 22 2013


REFERENCES

R. P. Stanley, Enumerative Combinatorics I, 2nd. ed., p. 247.


LINKS

Table of n, a(n) for n=1..9.


PROG

(Sage) for n in range(1, 10): print len([P for P in Posets(n) if P.is_selfdual()]) # Jori Mäntysalo, Oct 02 2014


CROSSREFS

Cf. A000112.
Sequence in context: A006882 A080498 A148013 * A005162 A129108 A230284
Adjacent sequences: A133980 A133981 A133982 * A133984 A133985 A133986


KEYWORD

nonn,more


AUTHOR

Richard Stanley, Jan 08 2008


EXTENSIONS

a(9) from Jori Mäntysalo, Oct 02 2014


STATUS

approved



