Number of restricted circular combinations.

Terms

a(0) =1a(1) =3a(2) =9a(3) =12a(4) =16a(5) =28a(6) =49a(7) =77a(8) =121a(9) =198a(10) =324a(11) =522a(12) =841a(13) =1363a(14) =2209a(15) =3572a(16) =5776a(17) =9348a(18) =15129a(19) =24477a(20) =39601a(21) =64078a(22) =103684a(23) =167762a(24) =271441a(25) =439203a(26) =710649a(27) =1149852a(28) =1860496a(29) =3010348