See A134457.

Terms

a(0) =0a(1) =1a(2) =1a(3) =2a(4) =6a(5) =6a(6) =11a(7) =22a(8) =44a(9) =92a(10) =92a(11) =157a(12) =311a(13) =622a(14) =1239a(15) =2478a(16) =4956a(17) =9912a(18) =19832a(19) =19832a(20) =36217a(21) =72058a(22) =144061a(23) =288122a(24) =576123a(25) =1152239a(26) =2304478a(27) =4608943