Number of necklaces with n beads of 3 colors, allowing turning over.

Terms

a(0) =1a(1) =3a(2) =6a(3) =10a(4) =21a(5) =39a(6) =92a(7) =198a(8) =498a(9) =1219a(10) =3210a(11) =8418a(12) =22913a(13) =62415a(14) =173088a(15) =481598a(16) =1351983a(17) =3808083a(18) =10781954a(19) =30615354a(20) =87230157a(21) =249144711a(22) =713387076a(23) =2046856566a(24) =5884491500a(25) =16946569371a(26) =48883660146a(27) =141217160458a(28) =408519019449