A043012 n-th base 6 palindrome that starts with 3.

3, 21, 111, 117, 123, 129, 135, 141, 651, 693, 735, 777, 819, 861, 3891, 3927, 3963, 3999, 4035, 4071, 4113, 4149, 4185, 4221, 4257, 4293, 4335, 4371, 4407, 4443, 4479, 4515, 4557, 4593, 4629, 4665, 4701, 4737, 4779, 4815