A248715 Isolated numbers: Mark the lowest number that doesn't touch a number that has already been mark on grid of number spiraling outward.

1, 10, 12, 15, 17, 19, 21, 23, 31, 48, 50, 52, 54, 60, 62, 64, 67, 69, 71, 73, 75, 77, 89, 91, 93, 101, 118, 120, 122, 124, 126, 128, 138, 140, 142, 148, 150, 152, 154, 156, 159, 161, 163, 179, 181, 183, 185, 187, 195, 197, 199, 211, 220, 222, 224, 226, 228

Offset

1,2

Comments

Start by creating a grid of integers starting with 1 in the center and spiraling outward.

.

64--63--62--61--60--59--58--57

|

37--36--35--34--33--32--31 56

| | |

38 17--16--15--14--13 30 55

| | | | |

39 18 5---4---3 12 29 54

| | | | | | |

40 19 6 1---2 11 28 53

| | | | | |

41 20 7---8---9--10 27 52

| | | |

42 21--22--23--24--25--26 51

| |

43--44--45--46--47--48--49--50

.

Then starting with 1 mark all numbers that have no neighboring marked numbers.

.

. 64 __ 62 __ 60 __ __ __

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. __ __ __ __ __ __ 31 __

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. __ 17 __ 15 __ __ __ __

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. __ __ __ __ __ 12 __ 54

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. __ 19 __ 1 __ __ __ __

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. __ __ __ __ __ 10 __ 52

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. __ 21 __ 23 __ __ __ __

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. __ __ __ __ __ 48 __ 50

Links

Michael P. Tilley, Table of n, a(n) for n = 1..10383

Michael P. Tilley, Image of a 204 X 204 grid

Crossrefs

Sequence in context: A343598 A006793 A308268 * A054518 A072198 A057485

Adjacent sequences: A248712 A248713 A248714 * A248716 A248717 A248718

Keyword

nonn

Author

Michael P. Tilley, Oct 12 2014

Status

approved