Number of secondary structures of size n with no stacks of length >=2.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =4a(5) =7a(6) =14a(7) =30a(8) =63a(9) =135a(10) =297a(11) =658a(12) =1470a(13) =3319a(14) =7547a(15) =17263a(16) =39722a(17) =91863a(18) =213379a(19) =497645a(20) =1164859a(21) =2735602a(22) =6443750a(23) =15220275a(24) =36041685a(25) =85546359a(26) =203486990a(27) =485000849a(28) =1158133257a(29) =2770323361