Number of bracelets (turnover necklaces) of n beads of 2 colors, 7 of them black.

Terms

a(0) =1a(1) =1a(2) =4a(3) =8a(4) =20a(5) =38a(6) =76a(7) =133a(8) =232a(9) =375a(10) =600a(11) =912a(12) =1368a(13) =1980a(14) =2829a(15) =3936a(16) =5412a(17) =7293a(18) =9724a(19) =12760a(20) =16588a(21) =21287a(22) =27092a(23) =34112a(24) =42640a(25) =52819a(26) =65008a(27) =79392a(28) =96405a(29) =116280