Number of ternary necklaces of length n with no subsequence 00.

Terms

a(0) =2a(1) =5a(2) =8a(3) =17a(4) =32a(5) =76a(6) =164a(7) =398a(8) =948a(9) =2336a(10) =5756a(11) =14460a(12) =36344a(13) =92282a(14) =235120a(15) =602348a(16) =1548320a(17) =3995602a(18) =10340300a(19) =26838896a(20) =69830576a(21) =182111414a(22) =475898036a(23) =1246011050a(24) =3267979208a(25) =8584907756a(26) =22585675348a(27) =59501499506a(28) =156955442072