Number of periodic palindromic structures of length n using exactly two different symbols.

Terms

a(0) =0a(1) =1a(2) =1a(3) =3a(4) =3a(5) =6a(6) =7a(7) =13a(8) =15a(9) =25a(10) =31a(11) =50a(12) =63a(13) =99a(14) =127a(15) =197a(16) =255a(17) =391a(18) =511a(19) =777a(20) =1023a(21) =1551a(22) =2047a(23) =3090a(24) =4095a(25) =6175a(26) =8191a(27) =12323a(28) =16383a(29) =24639