Explanation:
you made a typo.
since we are using only the digits 1, 3, 6 and 9, the list has to start
1, 3, 6, 9, 11, 13, 16, 19, 31, 33
it has to continue with
36, 39
we can skip the 40s and 50s and have then
61, 63, 66, 69
we can skip the 70s and 80s and have then
91, 93, 96, 99
that means we have 20 (5×4) numbers for the first 100.
we would have the corresponding 20 numbers in the 100s. like 101, 103, ...
but we have to skip 101, 103, 106, 109, because they contain 0.
so, it is only 16 numbers in the 100s.
there are none in the 200s.
then again 16 in the 300s. and the 600s and 900s.
so, we have
20 + 4×16 = 84 numbers in the first 1000.
then we have
16 in each the 1100s, the 1300s, the 1600s and 1900s.
and we have none in the 2000s.
so, in total we have
84 + 4×16 = 84 + 64 = 148 numbers to write.