a(n) = s(2n) - s(2n-1), where s( ) is sequence A023629.

Terms

a(0) =3a(1) =2a(2) =4a(3) =4a(4) =2a(5) =2a(6) =4a(7) =2a(8) =2a(9) =4a(10) =4a(11) =4a(12) =2a(13) =2a(14) =4a(15) =4a(16) =4a(17) =2a(18) =2a(19) =4a(20) =2a(21) =2a(22) =4a(23) =2a(24) =2a(25) =4a(26) =4a(27) =4a(28) =2a(29) =2