A bisection of A006921.

Terms

a(0) =1a(1) =3a(2) =7a(3) =13a(4) =29a(5) =55a(6) =115a(7) =209a(8) =465a(9) =883a(10) =1847a(11) =3357a(12) =7437a(13) =14087a(14) =29443a(15) =53505a(16) =119041a(17) =226051a(18) =472839a(19) =859405a(20) =1903901a(21) =3606327a(22) =7537523a(23) =13697489a(24) =30474449a(25) =57868403a(26) =121045047a(27) =220004381a(28) =487391245a(29) =923205639