a(n) = r*a(ceiling(n/2))+s*a(floor(n/2)) with a(1)=1 and (r,s)=(4,1).

Terms

a(0) =1a(1) =5a(2) =21a(3) =25a(4) =89a(5) =105a(6) =121a(7) =125a(8) =381a(9) =445a(10) =509a(11) =525a(12) =589a(13) =605a(14) =621a(15) =625a(16) =1649a(17) =1905a(18) =2161a(19) =2225a(20) =2481a(21) =2545a(22) =2609a(23) =2625a(24) =2881a(25) =2945a(26) =3009a(27) =3025a(28) =3089a(29) =3105