Generalized Euler phi function (for p=2).

Terms

a(0) =1a(1) =2a(2) =3a(3) =8a(4) =15a(5) =24a(6) =49a(7) =128a(8) =189a(9) =480a(10) =1023a(11) =1536a(12) =4095a(13) =6272a(14) =10125a(15) =32768a(16) =65025a(17) =96768a(18) =262143a(19) =491520a(20) =583443a(21) =2095104a(22) =4190209a(23) =6291456a(24) =15728625a(25) =33546240a(26) =49545027a(27) =102760448a(28) =268435455a(29) =331776000