A257324 - OEIS

A257324

Construct spiral of numbers on square grid as in Comments; sequence gives terms along the "7" arm.

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

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: A201329 A084000 A168197 * A138859 A257328 A361416

Adjacent sequences: A257321 A257322 A257323 * A257325 A257326 A257327

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Apr 21 2015

EXTENSIONS

More terms from Lars Blomberg, Apr 27 2015

STATUS

approved