Number of bracelets (turnover necklaces) of n beads of 2 colors, 11 of them black.

Terms

a(0) =1a(1) =1a(2) =6a(3) =16a(4) =56a(5) =147a(6) =392a(7) =912a(8) =2052a(9) =4262a(10) =8524a(11) =16159a(12) =29624a(13) =52234a(14) =89544a(15) =148976a(16) =242086a(17) =384111a(18) =597506a(19) =911456a(20) =1367184a(21) =2017509a(22) =2934559a(23) =4209504a(24) =5963464a(25) =8347612a(26) =11558232a(27) =15837472a(28) =21493712a(29) =28903332