Number of secondary structures of size n having no stacks of length 3.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =4a(5) =8a(6) =17a(7) =36a(8) =79a(9) =179a(10) =407a(11) =935a(12) =2173a(13) =5089a(14) =12005a(15) =28500a(16) =68022a(17) =163154a(18) =393060a(19) =950652a(20) =2307454a(21) =5618906a(22) =13723145a(23) =33607242a(24) =82507764a(25) =203028034a(26) =500659653a(27) =1237053269a(28) =3062204227a(29) =7593229687