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

Author

Michael P. Tilley, Oct 12 2014

Keywords

• nonn

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

.

. 31

.

. 17 15

.

. 12 54

.

. 19 1

.

. 10 52

.

. 21 23

.

. 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