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A257324
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Construct spiral of numbers on square grid as in Comments; sequence gives terms along the "7" arm.
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4
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7, 3, 11, 3, 2, 11, 2, 11, 2, 5, 7, 2, 3, 11, 3, 5, 3, 7, 5, 7, 3, 7, 3, 2, 5, 2, 7, 2, 3, 11, 3, 2, 5, 2, 5, 2, 5, 7, 2, 7, 2, 7, 2, 11, 2, 5, 7, 3, 7, 3, 5, 3, 5, 7, 2, 3, 5, 3, 5, 3, 5, 3, 11, 3, 2, 7, 3, 7, 3, 7, 5, 7, 3, 7, 3, 2, 5, 2, 5, 2, 5, 2, 7, 2, 7
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OFFSET
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1,1
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COMMENTS
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Place numbers 2,3,5,7 clockwise around a grid point (see illustrations in links). Divide grid into four spiral arms.
Extend each arm one step at a time, in rotation: first the 2 arm, then the 3 arm, then the 5 arm, then the 7 arm, then the 2 arm, etc.
Rule for extending: next term in arm is smallest number such that each cell in the grid is relatively prime to its eight neighbors.
Repetitions in arms are permitted.
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LINKS
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Popular Computing (Calabasas, CA), Problem 146: Gcd, Vol. 4 (No. 45, Dec 1976), page PC45-4.
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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