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A119495
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Number of bi-secondary structures of size N.
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0
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1, 1, 1, 2, 5, 13, 37, 112, 365, 1253, 4542, 17149, 67455, 274134, 1150125
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,4
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COMMENTS
| 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.
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EXAMPLE
| Encoding the secondary structure on the first halfplane with '()', on the 2nd with '[]' and unpaired bases with '-'. For n=4, bss(n)=5:
.... (.). (..) .(.) ([)]
Notice that '[(])' must not be counted, as it is isomorphic to '([)]'.
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CROSSREFS
| Cf. A004148.
Sequence in context: A151442 A053732 A170941 * A148301 A205544 A149855
Adjacent sequences: A119492 A119493 A119494 * A119496 A119497 A119498
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KEYWORD
| easy,nonn
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AUTHOR
| Yann Ponty (Yann.Ponty(AT)lri.fr), May 25 2006
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