a(0)=1, a(2n) = 2a(2n-1)+a(n), a(2n+1) = 2a(2n)+2a(n).

Terms

a(0) =1a(1) =4a(2) =12a(3) =32a(4) =76a(5) =176a(6) =384a(7) =832a(8) =1740a(9) =3632a(10) =7440a(11) =15232a(12) =30848a(13) =62464a(14) =125760a(15) =253184a(16) =508108a(17) =1019696a(18) =2043024a(19) =4093312a(20) =8194064a(21) =16403008a(22) =32821248a(23) =65672960a(24) =131376768a(25) =262815232a(26) =525692928a(27) =1051510784a(28) =2103147328