A043056 a(n)=(s(n)+3)/6, where s(n)=nth base 6 palindrome that starts with 3.

1, 4, 19, 20, 21, 22, 23, 24, 109, 116, 123, 130, 137, 144, 649, 655, 661, 667, 673, 679, 686, 692, 698, 704, 710, 716, 723, 729, 735, 741, 747, 753, 760, 766, 772, 778, 784, 790, 797, 803, 809, 815, 821, 827, 834, 840, 846, 852