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Regarding 1) I don't know of any good book, but this essay "Group Theory in the Bedroom" by Brian Hayes

http://www.americanscientist.org/issues/pub/group-theory-in-the-bedroom

is elementary and entertaining. A collection of his essays is published in book form under the same title.

Regarding 2), I like 'The Higher Arithmetic' by Davenport.

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Regarding 1) I don't know of any good book, but this essay "Group Theory in the Bedroom" by Brian Hayes

http://www.americanscientist.org/issues/pub/group-theory-in-the-bedroom

is elementary and entertaining. A collection of his essays is published in book form under the same title.