a(0) = 9, a(1) = 9, and a(n) = 3*a(n-1) - a(n-2) - 4 for n >= 2.

Terms

a(0) =9a(1) =9a(2) =14a(3) =29a(4) =69a(5) =174a(6) =449a(7) =1169a(8) =3054a(9) =7989a(10) =20909a(11) =54734a(12) =143289a(13) =375129a(14) =982094a(15) =2571149a(16) =6731349a(17) =17622894a(18) =46137329a(19) =120789089a(20) =316229934a(21) =827900709a(22) =2167472189a(23) =5674515854a(24) =14856075369a(25) =38893710249a(26) =101825055374a(27) =266581455869a(28) =697919312229