Number of necklaces with n beads of 3 colors, no 2 adjacent beads the same color.

Terms

a(0) =3a(1) =3a(2) =2a(3) =6a(4) =6a(5) =14a(6) =18a(7) =36a(8) =58a(9) =108a(10) =186a(11) =352a(12) =630a(13) =1182a(14) =2190a(15) =4116a(16) =7710a(17) =14602a(18) =27594a(19) =52488a(20) =99878a(21) =190746a(22) =364722a(23) =699252a(24) =1342182a(25) =2581428a(26) =4971066a(27) =9587580a(28) =18512790a(29) =35792568