A257340 - OEIS

A257340

Arrange numbers in a single clockwise spiral so that each number is relatively prime to its four (N,S,E,W) neighbors.

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 12, 17, 15, 14, 19, 16, 23, 18, 25, 22, 21, 20, 27, 26, 29, 24, 31, 35, 32, 37, 28, 41, 33, 34, 39, 40, 43, 30, 47, 36, 49, 38, 45, 44, 51, 46, 53, 42, 55, 48, 59, 50, 57, 61, 52, 63, 58, 65, 54, 67, 69, 56, 71, 62, 73

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

COMMENTS

Start with 1; always choose smallest number which has not yet appeared.

It is conjectured that every number appears.

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

EXAMPLE

. | -4 | -3 | -2 | -1 | 0 | +1 | +2 | +3 | +4 | +5

. ---+--------+----+----+----+----+----+----+----+----+----

. |

. | +------------------------------------------------

. +4 | | 83 68 75 74 81 70 87 76 85 ...

. ---+ | +---------------------------------------+

. +3 | | 66 | 49 38 45 44 51 46 53 42 |

. ---+ | | +-----------------------------+ |

. +2 | | 79 | 36 | 25 22 21 20 27 26 | 55 |

. ---+ | | | +-------------------+ | |

. +1 | | 64 | 47 | 18 | 7 8 9 10 | 29 | 48 |

. ---+ | | | | +---------+ | | |

. 0 | | 77 | 30 | 23 | 6 | 1 2 | 11 | 24 | 59 |

. ---+ | | | | +----o | | | |

. -1 | | 60 | 43 | 16 | 5 4 3 | 13 | 31 | 50 |

. ---+ | | | +--------------+ | | |

. -2 | | 73 | 40 | 19 14 15 17 12 | 35 | 57 |

. ---+ | | +------------------------+ | |

. -3 | | 62 | 39 34 33 41 28 37 32 | 61 |

. ---+ | +----------------------------------+ |

. -4 | | 71 56 69 67 54 65 58 63 52 |

. ---+ +--------------------------------------------+

CROSSREFS

Cf. A064413, A257321-A257339.

Sequence in context: A341537 A086044 A257456 * A194974 A302839 A130572

Adjacent sequences: A257337 A257338 A257339 * A257341 A257342 A257343

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Apr 21 2015

EXTENSIONS

More terms from Jon E. Schoenfield, Apr 23 2015

STATUS

approved