Number of ternary cubefree words of length n.

Terms

a(0) =1a(1) =3a(2) =9a(3) =24a(4) =66a(5) =180a(6) =486a(7) =1314a(8) =3558a(9) =9606a(10) =25956a(11) =70134a(12) =189462a(13) =511866a(14) =1382880a(15) =3735888a(16) =10092762a(17) =27266340a(18) =73661610a(19) =199001490a(20) =537615066a(21) =1452399978a(22) =3923748270