2n+3^n+5^n.

Terms

a(0) =2a(1) =10a(2) =38a(3) =158a(4) =714a(5) =3378a(6) =16366a(7) =80326a(8) =397202a(9) =1972826a(10) =9824694a(11) =49005294a(12) =244672090a(13) =1222297474a(14) =6108298622a(15) =30531927062a(16) =152630937378a(17) =763068593322