Number of primitive (period n) periodic palindromes using a maximum of two different symbols.

Terms

a(0) =2a(1) =1a(2) =2a(3) =3a(4) =6a(5) =7a(6) =14a(7) =18a(8) =28a(9) =39a(10) =62a(11) =81a(12) =126a(13) =175a(14) =246a(15) =360a(16) =510a(17) =728a(18) =1022a(19) =1485a(20) =2030a(21) =3007a(22) =4094a(23) =6030a(24) =8184a(25) =12159a(26) =16352a(27) =24381a(28) =32766a(29) =48849