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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

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Last modified August 22 16:17 EDT 2019. Contains 326178 sequences. (Running on oeis4.)