Riddles, brain puzzles and mathematical problems

[CarnivorousJelly]

8D I feel smart now >u<

Also, I feel like I should contribute... maybe

A man leaves an $100 dollar bill on his desk and leaves work. When he returns the money is gone. He has three suspects: the cook, the maid, and the mail man. The cook says he put the money under a book on his desk to keep it safe. They check and it is no longer there. The maid says she moved it when she was cleaning to the inside of the book between page 1 and 2. They open the book and look between page number 1 and 2 but it isn't there. The mail guy says he saw it sticking out of the book and to keep it safe he moved it to between page number 2 and 3.

Who stole the money and how do you know?

To clarify: they do not have to check the book a second time to know who stole it.

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What's the next number in this sequence?

1
11
21
1211
111221
312211