Palindromes in factorial base.

Terms

a(0) =0a(1) =1a(2) =3a(3) =7a(4) =9a(5) =11a(6) =25a(7) =33a(8) =41a(9) =121a(10) =127a(11) =133a(12) =139a(13) =147a(14) =153a(15) =159a(16) =165a(17) =173a(18) =179a(19) =185a(20) =191a(21) =721a(22) =751a(23) =781a(24) =811a(25) =843a(26) =873a(27) =903a(28) =933a(29) =965