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A307838
Counterclockwise square spiral constructed by greedy algorithm such that the product of the values of any two vertically or horizontally adjacent cells is unique.
2
1, 1, 2, 3, 3, 4, 2, 5, 7, 2, 11, 8, 3, 9, 5, 10, 2, 13, 7, 16, 3, 17, 5, 8, 18, 3, 19, 4, 13, 11, 5, 14, 7, 12, 8, 23, 1, 29, 5, 15, 8, 22, 5, 23, 4, 18, 17, 6, 26, 5, 27, 6, 25, 9, 11, 19, 1, 31, 9, 17, 11, 20, 7, 21, 8, 37, 3, 41, 11, 24, 9, 35, 6, 34, 10
OFFSET
0,3
COMMENTS
This sequence is a two-dimensional variant of A088177.
Visually, we have a superposition of two images that we can separate by considering the parity of the sum of the x and y coordinates (see illustrations in Links section).
EXAMPLE
The spiral begins:
7---19---16---29---14---22---13---43----3---47----2
| |
31 8---21----7---20---11---17----9---31----1 43
| | | |
2 37 1---23----8---12----7---14----5 19 14
| | | | | |
53 3 29 2---10----5----9----3 11 11 14
| | | | | | | |
4 41 5 13 3----3----2 8 13 9 21
| | | | | | | | | |
37 11 15 7 4 1----1 11 4 25 11
| | | | | | | | |
10 24 8 16 2----5----7----2 19 6 31
| | | | | | |
19 9 22 3---17----5----8---18----3 27 10
| | | | |
12 35 5---23----4---18---17----6---26----5 25
| | |
23 6---34---10---29---13----1---41----7---36----8
|
9---29----8---26---12---25---49----8---32---10---43
PROG
(PARI) See Links section.
CROSSREFS
See A307834 for the additive variant.
Cf. A088177.
Sequence in context: A269526 A106448 A295280 * A159909 A176004 A214738
KEYWORD
nonn
AUTHOR
Rémy Sigrist, May 01 2019
STATUS
approved