a(n) = 5*3^n - 4*2^n.

Terms

a(0) =1a(1) =7a(2) =29a(3) =103a(4) =341a(5) =1087a(6) =3389a(7) =10423a(8) =31781a(9) =96367a(10) =291149a(11) =877543a(12) =2640821a(13) =7938847a(14) =23849309a(15) =71613463a(16) =214971461a(17) =645176527a(18) =1936053869a(19) =5809210183a(20) =17429727701a(21) =52293377407a(22) =156888520829a(23) =470682339703