Palindromes in base 4 (written in base 4).

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =11a(5) =22a(6) =33a(7) =101a(8) =111a(9) =121a(10) =131a(11) =202a(12) =212a(13) =222a(14) =232a(15) =303a(16) =313a(17) =323a(18) =333a(19) =1001a(20) =1111a(21) =1221a(22) =1331a(23) =2002a(24) =2112a(25) =2222a(26) =2332a(27) =3003a(28) =3113a(29) =3223