A010062(2^n-1).

Terms

a(0) =1a(1) =2a(2) =5a(3) =14a(4) =38a(5) =92a(6) =216a(7) =518a(8) =1165a(9) =2641a(10) =5981a(11) =13215a(12) =28880a(13) =62481a(14) =133539a(15) =281878a(16) =595867a(17) =1257995a(18) =2656439a(19) =5585174a(20) =11751388a(21) =24708442a(22) =51644779a(23) =107729838a(24) =224507391a(25) =467923765a(26) =971364960a(27) =2016542071