I thought of the reason independently: it’s that if the number before 66 is not odd, but even instead, it must be either 2 or 4, since if it was 6 then the sequence would have had a double 6 one digit earlier.
I thought of the reason independently: it’s that if the number before 66 is not odd, but even instead, it must be either 2 or 4, since if it was 6 then the sequence would have had a double 6 one digit earlier.