Number of nonempty subsets of {1, ..., n} containing no two cyclically successive elements.

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =6a(5) =10a(6) =17a(7) =28a(8) =46a(9) =75a(10) =122a(11) =198a(12) =321a(13) =520a(14) =842a(15) =1363a(16) =2206a(17) =3570a(18) =5777a(19) =9348a(20) =15126a(21) =24475a(22) =39602a(23) =64078a(24) =103681a(25) =167760a(26) =271442a(27) =439203a(28) =710646a(29) =1149850