nothing random about 19, he's generating the terms with a sequence
20.) 12, actually lcm (4,3)=12
21.) 35, 7*5=35
22.) all multiples of 28
=1*28 (1 box of 28/ 28 boxes of 1)
=2*14 (14 boxes of 2/ 2 boxes of 14)
=4*7
actually 28=2^2 * 7 by Fundamental Thm of Arithmetic
2*2*7
2*14
4*7
28*1
so there are 4 ways depending on how you arrange boxes and crayones, excluding 1,28
