"BIK" (reversible, indistinct, unlabeled) transform of A000237.

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =15a(5) =48a(6) =164a(7) =583a(8) =2142a(9) =8062a(10) =30950a(11) =120651a(12) =476418a(13) =1901311a(14) =7656763a(15) =31074151a(16) =126963466a(17) =521820340a(18) =2155911512a(19) =8948711597a(20) =37299355151a(21) =156054201936a(22) =655134261795