a(n) = T(n,2), array T as in A054134.

Terms

a(0) =2a(1) =6a(2) =18a(3) =46a(4) =107a(5) =235a(6) =498a(7) =1032a(8) =2109a(9) =4273a(10) =8612a(11) =17302a(12) =34695a(13) =69495a(14) =139110a(15) =278356a(16) =556865a(17) =1113901a(18) =2227992a(19) =4456194a(20) =8912619a(21) =17825491a(22) =35651258a(23) =71302816a(24) =142605957a(25) =285212265a(26) =570424908a(27) =1140850222a(28) =2281700879