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A257322 Construct spiral of numbers on square grid as in Comments; sequence gives terms along the "3" arm. 4
3, 2, 7, 3, 5, 7, 3, 7, 3, 2, 11, 3, 11, 3, 2, 5, 2, 7, 2, 7, 2, 11, 2, 5, 7, 3, 5, 7, 2, 11, 3, 5, 3, 5, 3, 5, 3, 7, 3, 7, 5, 7, 3, 7, 3, 2, 5, 2, 5, 2, 7, 2, 7, 2, 3, 11, 3, 2, 5, 2, 5, 2, 5, 7, 3, 5, 7, 2, 7, 2, 7, 2, 7, 2, 5, 11, 7, 3, 7, 3, 7, 3, 5, 3, 5 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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.

The four arms are A257321, A257322, A257323, A257324.

LINKS

Lars Blomberg, Table of n, a(n) for n = 1..10000

Popular Computing (Calabasas, CA), Problem 146: Gcd, Vol. 4 (No. 45, Dec 1976), page PC45-4.

N. J. A. Sloane, Spirals showing initial terms of A257321-A257332

CROSSREFS

Cf. A064413, A257321-A257340.

Sequence in context: A071190 A295314 A057020 * A276466 A289336 A324509

Adjacent sequences:  A257319 A257320 A257321 * A257323 A257324 A257325

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Apr 21 2015

EXTENSIONS

More terms from Lars Blomberg, Apr 27 2015

STATUS

approved

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Last modified August 8 06:27 EDT 2020. Contains 336290 sequences. (Running on oeis4.)