G.f.: x*(1 - x + x^2)/((1-x)^2 * (1 - x - x^2)).

Terms

a(0) =0a(1) =1a(2) =2a(3) =5a(4) =10a(5) =19a(6) =34a(7) =59a(8) =100a(9) =167a(10) =276a(11) =453a(12) =740a(13) =1205a(14) =1958a(15) =3177a(16) =5150a(17) =8343a(18) =13510a(19) =21871a(20) =35400a(21) =57291a(22) =92712a(23) =150025a(24) =242760a(25) =392809a(26) =635594a(27) =1028429a(28) =1664050a(29) =2692507