%I A006860 M2959
%S A006860 1,3,13,111,1381,25623,678133,26269735,1447451707,114973020921,13034306495563
%N A006860 Tiered orders on n nodes.
%D A006860 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A006860 G. Kreweras, Denombrement des ordres etages, Discrete Math., 53 (1985), 
               147-149.
%Y A006860 Sequence in context: A098027 A073587 A061377 this_sequence A090537 A063269 
               A098406
%Y A006860 Adjacent sequences: A006857 A006858 A006859 this_sequence A006861 A006862 
               A006863
%K A006860 nonn
%O A006860 1,2
%A A006860 Simon Plouffe (simon.plouffe(AT)gmail.com)