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%I #15 Mar 07 2020 12:24:31
%S 1,2,3,8,15,50,119,493,1521
%N Number of nonisomorphic n-element self-dual posets (or partially ordered sets).
%C Posets whose Hasse diagram looks the same if it is turned upside down. - _N. J. A. Sloane_, Mar 22 2013
%D R. P. Stanley, Enumerative Combinatorics I, 2nd. ed., p. 247.
%o (Sage) for n in range(1,10): print(len([P for P in Posets(n) if P.is_selfdual()])) # _Jori Mäntysalo_, Oct 02 2014
%Y Cf. A000112.
%K nonn,more
%O 1,2
%A _Richard Stanley_, Jan 08 2008
%E a(9) from _Jori Mäntysalo_, Oct 02 2014
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