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%I #10 Jan 02 2016 14:02:35
%S 1,2,9,126,13596,108096891
%N Number of reduced contexts on n unlabeled objects.
%C Equivalently, number of closure systems on n points, up to isomorphism.
%D Bernhard Ganter, Rudolf Wille: Formal Concept Analysis, Springer-Verlag, 1999, ISBN 3-540-62771-5, p. 59.
%K hard,nonn,nice
%O 1,2
%A Bernhard Ganter (ganter(AT)math.tu-dresden.de)
%E a(6) from _Klaus Hoffmann_, Jan 01 2016