A253104(2^n-1).

Terms

a(0) =1a(1) =8a(2) =32a(3) =140a(4) =580a(5) =2300a(6) =9212a(7) =36708a(8) =145684a(9) =579132a(10) =2300748a(11) =9136868a(12) =36293220a(13) =144150716a(14) =572523772a(15) =2273961796a(16) =9031663444a(17) =35871633244a(18) =142474173772a(19) =565874928900