(A122536(n)-A003000(n))/2.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =0a(8) =0a(9) =1a(10) =2a(11) =4a(12) =8a(13) =18a(14) =36a(15) =73a(16) =146a(17) =295a(18) =590a(19) =1182a(20) =2364a(21) =4732a(22) =9464a(23) =18929a(24) =37858a(25) =75721a(26) =151442a(27) =302878a(28) =605756a(29) =1211504