A000013 / 2.

Terms

a(0) =1a(1) =1a(2) =2a(3) =2a(4) =4a(5) =5a(6) =10a(7) =15a(8) =28a(9) =47a(10) =90a(11) =158a(12) =298a(13) =548a(14) =1034a(15) =1928a(16) =3658a(17) =6899a(18) =13136a(19) =24970a(20) =47710a(21) =91181a(22) =174858a(23) =335546a(24) =645436a(25) =1242767a(26) =2397044a(27) =4628198a(28) =8948416a(29) =17318417