A257332 -id:A257332 - cp's OEIS frontend

A257327 Construct spiral of numbers on square grid as in Comments; sequence gives terms along the "5" arm.

5, 2, 11, 4, 7, 13, 8, 17, 19, 3, 23, 9, 29, 21, 31, 15, 14, 37, 27, 41, 43, 16, 33, 26, 25, 6, 47, 12, 53, 22, 49, 10, 39, 35, 51, 59, 57, 61, 63, 65, 67, 20, 71, 73, 69, 79, 45, 83, 85, 28, 89, 97, 77, 75, 91, 55, 81, 101, 87, 95, 32, 103, 38, 107, 18, 109

Offset: 1

N. J. A. Sloane, Apr 21 2015

nonn

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. Inside an arm, the terms must be distinct.
Repetitions between arms are permitted.
The four arms are A257325, A257326, A257327, A257328.

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

Cf. A064413, A257321-A257340.

More terms from Lars Blomberg, Apr 27 2015

A257328 Construct spiral of numbers on square grid as in Comments; sequence gives terms along the "7" arm.

Original entry on oeis.org

7, 3, 11, 9, 2, 13, 4, 5, 8, 17, 19, 10, 21, 23, 25, 29, 31, 35, 37, 15, 41, 43, 47, 16, 53, 20, 59, 22, 49, 61, 27, 14, 55, 26, 67, 28, 33, 65, 32, 71, 34, 73, 38, 79, 44, 83, 39, 77, 51, 89, 91, 57, 85, 97, 40, 63, 101, 103, 107, 109, 113, 95, 127, 115, 6

Offset: 1

N. J. A. Sloane, Apr 21 2015

nonn

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. Inside an arm, the terms must be distinct.
Repetitions between arms are permitted.
The four arms are A257325, A257326, A257327, A257328.

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

Cf. A064413, A257321-A257340.

More terms from Lars Blomberg, Apr 27 2015

cp's OEIS Frontend

A257327 Construct spiral of numbers on square grid as in Comments; sequence gives terms along the "5" arm.

Views

Author

Keywords

Comments

Links

Crossrefs

Extensions