Number of necklaces with 11 black beads and n-11 white beads.

Terms

a(0) =1a(1) =1a(2) =6a(3) =26a(4) =91a(5) =273a(6) =728a(7) =1768a(8) =3978a(9) =8398a(10) =16796a(11) =32066a(12) =58786a(13) =104006a(14) =178296a(15) =297160a(16) =482885a(17) =766935a(18) =1193010a(19) =1820910a(20) =2731365a(21) =4032015a(22) =5864750a(23) =8414640a(24) =11920740a(25) =16689036a(26) =23107896a(27) =31666376a(28) =42975796