a(n) = A255304(2^n-1).

Terms

a(0) =1a(1) =5a(2) =15a(3) =51a(4) =153a(5) =477a(6) =1431a(7) =4347a(8) =13041a(9) =39285a(10) =117855a(11) =354051a(12) =1062153a(13) =3187917a(14) =9563751a(15) =28695627a(16) =86086881a(17) =258273765a(18) =774821295a(19) =2324503251a(20) =6973509753a(21) =20920647357a(22) =62761942071a(23) =188286180507a(24) =564858541521