A119495 Number of bi-secondary structures of size N.

1, 1, 1, 2, 5, 13, 37, 112, 365, 1253, 4542, 17149, 67455, 274134, 1150125

Offset

0,4

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.

Links

Table of n, a(n) for n=0..14.

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 '([)]'.

Crossrefs

Cf. A004148.

Sequence in context: A216617 A243412 A170941 * A148301 A339039 A205544

Adjacent sequences: A119492 A119493 A119494 * A119496 A119497 A119498

Keyword

easy,nonn

Author

Yann Ponty (Yann.Ponty(AT)lri.fr), May 25 2006

Status

approved