Number of primitive (period n) bracelets using exactly two different colored beads.

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =6a(5) =8a(6) =16a(7) =24a(8) =42a(9) =69a(10) =124a(11) =208a(12) =378a(13) =668a(14) =1214a(15) =2220a(16) =4110a(17) =7630a(18) =14308a(19) =26931a(20) =50944a(21) =96782a(22) =184408a(23) =352450a(24) =675180a(25) =1296477a(26) =2493680a(27) =4805388a(28) =9272778a(29) =17919558