%I A119495
%S A119495 1,1,1,2,5,13,37,112,365,1253,4542,17149,67455,274134,1150125
%N A119495 Number of bi-secondary structures of size N.
%C A119495 A BiSecondary Structure(BSS) is a RNA graph that can be drawn without 
               crossings using at most two halfplanes. The numbers displayed here 
               were obtained by first generating all secondary structures of a given 
               size and then by carefully counting possible completions on the second 
               halfplane. Keep in mind that the simple shuffling of two secondary 
               structures would yield many isomorphic RNA graphs.
%e A119495 Encoding the secondary structure on the first halfplane with '()', on 
               the 2nd with '[]' and unpaired bases with '-'. For n=4, bss(n)=5:
%e A119495 .... (.). (..) .(.) ([)]
%e A119495 Notice that '[(])' must not be counted, as it is isomorphic to '([)]'.
%Y A119495 Cf. A004148.
%Y A119495 Sequence in context: A149854 A151442 A053732 this_sequence A148301 A149855 
               A149856
%Y A119495 Adjacent sequences: A119492 A119493 A119494 this_sequence A119496 A119497 
               A119498
%K A119495 easy,nonn
%O A119495 0,4
%A A119495 Yann Ponty (Yann.Ponty(AT)lri.fr), May 25 2006