A133983 Number of nonisomorphic n-element self-dual posets (or partially ordered sets).

1, 2, 3, 8, 15, 50, 119, 493, 1521

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 A350654 A129108

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