a(n) = r*a(ceiling(n/2))+s*a(floor(n/2)) with a(1)=1 and (r,s)=(3,2).

Terms

a(0) =1a(1) =5a(2) =17a(3) =25a(4) =61a(5) =85a(6) =109a(7) =125a(8) =233a(9) =305a(10) =377a(11) =425a(12) =497a(13) =545a(14) =593a(15) =625a(16) =949a(17) =1165a(18) =1381a(19) =1525a(20) =1741a(21) =1885a(22) =2029a(23) =2125a(24) =2341a(25) =2485a(26) =2629a(27) =2725a(28) =2869a(29) =2965