Jacobsthal gap sequence.

Terms

a(0) =0a(1) =1a(2) =3a(3) =1a(4) =15a(5) =1a(6) =63a(7) =1a(8) =255a(9) =1a(10) =1023a(11) =1a(12) =4095a(13) =1a(14) =16383a(15) =1a(16) =65535a(17) =1a(18) =262143a(19) =1a(20) =1048575a(21) =1a(22) =4194303a(23) =1a(24) =16777215a(25) =1a(26) =67108863a(27) =1a(28) =268435455a(29) =1