Number of base-3 circular n-digit numbers with adjacent digits differing by 1 or less.

Terms

a(0) =1a(1) =3a(2) =7a(3) =15a(4) =35a(5) =83a(6) =199a(7) =479a(8) =1155a(9) =2787a(10) =6727a(11) =16239a(12) =39203a(13) =94643a(14) =228487a(15) =551615a(16) =1331715a(17) =3215043a(18) =7761799a(19) =18738639a(20) =45239075a(21) =109216787a(22) =263672647a(23) =636562079a(24) =1536796803a(25) =3710155683a(26) =8957108167a(27) =21624372015a(28) =52205852195