Answer:
9, 13, 10, 11,  7, 3, 4.
Step-by-step explanation:
9, 13, 10, 11,  7, 3, 4 are the ones which should be shaded and can be seen from the top. In ascending order: 3, 4, 7, 9, 10, 11, 13. 
1, 2, 5, 6, 8, 12, 16, 14, 15 are the numbers of the boxes that would not be seen from the top. 
Hope this helps!