a(n) = 36*2^n + 9.

Terms

a(0) =45a(1) =81a(2) =153a(3) =297a(4) =585a(5) =1161a(6) =2313a(7) =4617a(8) =9225a(9) =18441a(10) =36873a(11) =73737a(12) =147465a(13) =294921a(14) =589833a(15) =1179657a(16) =2359305a(17) =4718601a(18) =9437193a(19) =18874377a(20) =37748745a(21) =75497481a(22) =150994953a(23) =301989897a(24) =603979785a(25) =1207959561a(26) =2415919113a(27) =4831838217a(28) =9663676425a(29) =19327352841