> Martin Gardner and AK Dewdney articles in old Scientific American magazines

All of Gardner's Scientific American columns are conveniently available on CD-ROM for under $40 [1].

[1] https://www.amazon.com/gp/product/0883855453

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> Practice, and read about similar puzzles/problems. Track down reprints/scans of Martin Gardner's Mathematical Games and similar publications.

The entire set of the 15 books that collected his "Mathematical Games" columns from Scientific American are available in PDF form on a CD-ROM:

http://www.amazon.com/Martin-Gardners-Mathematical-Games-Gar...