Number of secondary structures of size n having no stacks of length 2.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =4a(5) =7a(6) =14a(7) =31a(8) =66a(9) =142a(10) =316a(11) =708a(12) =1593a(13) =3625a(14) =8314a(15) =19165a(16) =44433a(17) =103557a(18) =242376a(19) =569514a(20) =1343099a(21) =3177766a(22) =7540845a(23) =17943506a(24) =42804078a(25) =102345017a(26) =245233366a(27) =588785677a(28) =1416247791a(29) =3412495415