Number of secondary structures of size n having no stacks of length 1.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =2a(6) =4a(7) =8a(8) =14a(9) =23a(10) =38a(11) =65a(12) =117a(13) =214a(14) =391a(15) =708a(16) =1278a(17) =2318a(18) =4238a(19) =7803a(20) =14419a(21) =26684a(22) =49433a(23) =91736a(24) =170656a(25) =318280a(26) =594905a(27) =1113868a(28) =2088554a(29) =3921505