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

Terms

a(0) =0a(1) =1a(2) =1a(3) =2a(4) =3a(5) =5a(6) =8a(7) =14a(8) =21a(9) =39a(10) =62a(11) =112a(12) =189a(13) =352a(14) =607a(15) =1144a(16) =2055a(17) =3885a(18) =7154a(19) =13602a(20) =25472a(21) =48670a(22) =92204a(23) =176770a(24) =337590a(25) =649341a(26) =1246840a(27) =2404872a(28) =4636389a(29) =8964143