login
This site is supported by donations to The OEIS Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A133983 Number of nonisomorphic n-element self-dual posets (or partially ordered sets). 1
1, 2, 3, 8, 15, 50, 119, 493, 1521 (list; graph; refs; listen; history; text; internal format)
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 14 03:31 EST 2019. Contains 329978 sequences. (Running on oeis4.)