a(n) = 6*a(n-2) + a(n-4), where a(0) = 2, a(1) = 8, a(2) = 13, a(3) = 49.

Terms

a(0) =2a(1) =8a(2) =13a(3) =49a(4) =80a(5) =302a(6) =493a(7) =1861a(8) =3038a(9) =11468a(10) =18721a(11) =70669a(12) =115364a(13) =435482a(14) =710905a(15) =2683561a(16) =4380794a(17) =16536848a(18) =26995669a(19) =101904649a(20) =166354808a(21) =627964742a(22) =1025124517a(23) =3869693101a(24) =6317101910a(25) =23846123348a(26) =38927735977a(27) =146946433189a(28) =239883517772a(29) =905524722482