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 A257323 Construct spiral of numbers on square grid as in Comments; sequence gives terms along the "5" arm. 4
 5, 2, 11, 2, 5, 7, 2, 5, 7, 3, 5, 3, 5, 3, 7, 3, 2, 11, 3, 5, 7, 2, 7, 2, 7, 2, 5, 2, 3, 2, 5, 2, 5, 7, 3, 7, 3, 5, 3, 5, 7, 2, 5, 7, 3, 7, 3, 7, 3, 2, 11, 3, 5, 3, 5, 3, 5, 3, 7, 3, 2, 5, 2, 5, 2, 7, 2, 7, 2, 3, 5, 7, 2, 7, 2, 7, 2, 7, 2, 5, 7, 3, 5, 11, 2, 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: A319408 A050004 A111187 * A293559 A094683 A094685 Adjacent sequences:  A257320 A257321 A257322 * A257324 A257325 A257326 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 January 26 20:02 EST 2022. Contains 350599 sequences. (Running on oeis4.)