Number of ways to tile vertically-fault-free 3 X n strip with squares and dominoes.

Terms

a(0) =1a(1) =3a(2) =13a(3) =26a(4) =66a(5) =154a(6) =380a(7) =904a(8) =2204a(9) =5286a(10) =12818a(11) =30854a(12) =74636a(13) =179948a(14) =434820a(15) =1049122a(16) =2533818a(17) =6115538a(18) =14766868a(19) =35646080a(20) =86064196a(21) =207766110a(22) =501609946a(23) =1210964110a(24) =2923573588a(25) =7058053972a(26) =17039774268