2. Find the six digits that are not allowed on the reverse side.

The possible situations of classification are as follows

This six-digit number contains two twos: the number of such six-digit numbers is 5 * 2 4 = 80.

②, including three twos: (2 * 3+3 * 2) * 2 3 (with only two bicontinuities)+4 * 2 3 (with three bicontinuities) = 128.

③, including four 2s (all unsatisfied): Yes15 * 2 2 = 60.

(4), including five twos: there are 6*2= 12.

⑤, including 6 2: Yes 1.

To sum up, the six-digit number that meets the conditions is 729-(80+128+60+12+1) = 448.