a(n) = 2^A000120(n) - 1.

Terms

a(0) =0a(1) =1a(2) =1a(3) =3a(4) =1a(5) =3a(6) =3a(7) =7a(8) =1a(9) =3a(10) =3a(11) =7a(12) =3a(13) =7a(14) =7a(15) =15a(16) =1a(17) =3a(18) =3a(19) =7a(20) =3a(21) =7a(22) =7a(23) =15a(24) =3a(25) =7a(26) =7a(27) =15a(28) =7a(29) =15