Use the three numbers 123 to make up four digits. Among the four digits that may be made up, how many are there at least two consecutive digits that are 2?

Classified discussion,
When there are two 2's,
There are six combinations with the first two digits of 2
There are four combinations with the second and third digit of 2
There are four combinations with the third and fourth digit 2
When there are three 2's,
There are two possibilities: the first two third digit is 2 or the second three fourth digit is 2
When there are four 2's, there is a possibility
So at least two consecutive digits of 2 have 6 + 4 + 4 + 2 + 1 = 17

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