Number of isolated 0's in all ternary words of length n on {0,1,2}.

Terms

a(0) =1a(1) =4a(2) =16a(3) =60a(4) =216a(5) =756a(6) =2592a(7) =8748a(8) =29160a(9) =96228a(10) =314928a(11) =1023516a(12) =3306744a(13) =10628820a(14) =34012224a(15) =108413964a(16) =344373768a(17) =1090516932a(18) =3443737680a(19) =10847773692a(20) =34093003032a(21) =106928054964a(22) =334731302496