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

1, 2, 3, 8, 15, 50, 119, 493, 1521, 7924, 30783, 209818

Offset: 1

Author

Richard Stanley, Jan 08 2008

Keywords

• nonn
• more

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.

Crossrefs

Cf. A000112.

Programs

Sage

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

Extensions

a(9) from Jori Mäntysalo, Oct 02 2014

a(10-12) from Rico Zöllner and Konrad Handrich, Oct 22 2024