Answer:
13, 17, 19
Explanation:
Go through (12-20) and find the multipliers for each number.
13 = 13 x 1
14 = 7 x 2 , 14 x1 = no
15 = 5 x 3, 15 x 1 = no
17 = 17 x 1
18 = 6 x 3, 9 x 2, 18 x 1 = no
19 = 19 x 1
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