a(n) = 2^n + 4^n + 5^n.

Terms

a(0) =3a(1) =11a(2) =45a(3) =197a(4) =897a(5) =4181a(6) =19785a(7) =94637a(8) =456417a(9) =2215781a(10) =10815225a(11) =53024477a(12) =260921937a(13) =1287820181a(14) =6371967465a(15) =31591352717a(16) =156882923457a(17) =780119453381