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