Numbers of the form i*4^j-1 (i=1..3, j >= 0).

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =7a(5) =11a(6) =15a(7) =31a(8) =47a(9) =63a(10) =127a(11) =191a(12) =255a(13) =511a(14) =767a(15) =1023a(16) =2047a(17) =3071a(18) =4095a(19) =8191a(20) =12287a(21) =16383a(22) =32767a(23) =49151a(24) =65535a(25) =131071a(26) =196607a(27) =262143a(28) =524287a(29) =786431