A255275(2^n-1).

Terms

a(0) =1a(1) =8a(2) =28a(3) =128a(4) =480a(5) =2008a(6) =7776a(7) =31672a(8) =124528a(9) =500792a(10) =1982144a(11) =7926808a(12) =31474832a(13) =125567832a(14) =499339552a(15) =1989964024a(16) =7918843056a(17) =31542845816a(18) =125560568192a(19) =500031498968