a(n) = A027306(n) + A027306(n-1) for n > 0; a(0) = 1.

Terms

a(0) =1a(1) =2a(2) =4a(3) =7a(4) =15a(5) =27a(6) =58a(7) =106a(8) =227a(9) =419a(10) =894a(11) =1662a(12) =3534a(13) =6606a(14) =14004a(15) =26292a(16) =55587a(17) =104739a(18) =220918a(19) =417526a(20) =878810a(21) =1665242a(22) =3498444a(23) =6644172a(24) =13934990a(25) =26517902a(26) =55531948a(27) =105863596a(28) =221384892a(29) =422711484