Answers

2016-06-23T16:58:26+08:00
2,3,5,7

23, 25, 27, 32, 52, 72, 35, 37, 53, 73, 57, 75 = 12 two digit numbers
32, 52, 72 = 3 two digit even numbers

If two digits can be repeated, we already have the 12 numbers.
22, 33, 55, 77 = 4 two digit numbers which digits are repeated.

Add 12 and 4 and we get 16 numbers.
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