Number of bi-secondary structures of size N.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =5a(5) =13a(6) =37a(7) =112a(8) =365a(9) =1253a(10) =4542a(11) =17149a(12) =67455a(13) =274134a(14) =1150125