Number of normal subgroups of dihedral group with 2n elements.

Terms

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