Unlabeled analog of A025168.

Terms

a(0) =0a(1) =1a(2) =3a(3) =8a(4) =21a(5) =54a(6) =137a(7) =344a(8) =856a(9) =2113a(10) =5179a(11) =12614a(12) =30548a(13) =73595a(14) =176455a(15) =421215a(16) =1001388a(17) =2371678a(18) =5597245a(19) =13166069a(20) =30873728a(21) =72185937a(22) =168313391a(23) =391428622a(24) =908058205a(25) =2101629502a(26) =4853215947a(27) =11183551059a(28) =25718677187a(29) =59030344851