A257333 -id:A257333 - cp's OEIS frontend

A257334 Construct spiral of numbers on square grid as in Comments; sequence gives terms along the "3" arm.

3, 2, 5, 4, 7, 8, 9, 11, 13, 6, 17, 10, 19, 14, 23, 12, 25, 16, 29, 15, 31, 22, 21, 20, 37, 18, 35, 24, 41, 26, 27, 28, 43, 32, 33, 34, 39, 38, 45, 44, 47, 30, 49, 36, 53, 40, 51, 46, 55, 42, 59, 48, 61, 50, 57, 52, 63, 58, 65, 54, 67, 56, 69, 71, 60, 73, 62

Offset: 1

N. J. A. Sloane, Apr 21 2015

nonn

Place numbers 2,3,4,5 clockwise around a grid point (see illustration in "Spiral" link). 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 4 arm, then the 5 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 four (N,S,E,W) neighbors. Inside an arm, the terms must be distinct.
Repetitions between arms are permitted.
The "2" arm is A257333, the "3" arm is the present sequence (A257334). The "4" arm begins 4,3,2,5, and thereafter agrees with the "2" arm. The "5" arm begins 5,2,3,4, and thereafter agrees with the "3" arm.

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, Spiral showing initial terms of A257333-A257334

Cf. A064413, A257321-A257340.

Corrected a(25), a(29), a(30), a(32) and more terms from Lars Blomberg, Apr 28 2015

cp's OEIS Frontend

A257334 Construct spiral of numbers on square grid as in Comments; sequence gives terms along the "3" arm.

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