a(n) = |{m : multiplicative order of 8 mod m = n}|.

Terms

a(0) =2a(1) =4a(2) =2a(3) =18a(4) =6a(5) =24a(6) =10a(7) =72a(8) =4a(9) =84a(10) =14a(11) =462a(12) =14a(13) =128a(14) =54a(15) =672a(16) =30a(17) =124a(18) =14a(19) =4494a(20) =82a(21) =364a(22) =14a(23) =7608a(24) =120a(25) =172a(26) =56a(27) =9054a(28) =62a(29) =3920