Number of bracelets of length n using exactly two different colored beads.

Terms

a(0) =0a(1) =1a(2) =2a(3) =4a(4) =6a(5) =11a(6) =16a(7) =28a(8) =44a(9) =76a(10) =124a(11) =222a(12) =378a(13) =685a(14) =1222a(15) =2248a(16) =4110a(17) =7683a(18) =14308a(19) =27010a(20) =50962a(21) =96907a(22) =184408a(23) =352696a(24) =675186a(25) =1296856a(26) =2493724a(27) =4806076a(28) =9272778a(29) =17920858