OFFSET
1,2
COMMENTS
Inverse function to A193838, which is the main entry for this problem.
REFERENCES
R. K. Guy, Unsolved Problems in Number Theory, Third Edition, Springer New York, 2004, F2, 367-368.
Keith F. Lynch, Posting to Math Fun Mailing List, Apr 02 2016.
LINKS
P. Erdős and R. K. Guy, Distinct distances between lattice points, Elemente der Mathematik 25 (1970), 121-123.
Wolfram Demonstration Project, No Repeated Distances
A. Zimmermann, Al Zimmermann's Programming Contests: Point Packing. (Oct 10, 2009).
EXAMPLE
From Ehit Dinesh Agarwal, May 28 2020: (Start)
An 11 X 11 grid has only two subsets of size 10, barring symmetry: {(0,0), (0,2), (0,3), (0,7), (1,10), (5,4), (6,0), (8,7), (9,8), (10, 10)} and {(0,0), (0,6), (0,7), (1,2), (4,10), (7,8), (7,10), (9,2), (9,6), (10,5)}.
A 12 x 13 grid has only four subsets of size 11, barring symmetry: {(0,0), (0,1), (0,9), (0,12), (2,0), (5,3), (6,12), (7,0), (8,4), (10,10), (11,11)}. (End)
CROSSREFS
KEYWORD
nonn,hard,more,nice
AUTHOR
N. J. A. Sloane, Apr 14 2016
EXTENSIONS
a(11)-a(13) corrected and extended by Ehit Dinesh Agarwal, May 28 2020
a(14)-a(16) from Bert Dobbelaere, Sep 20 2020
a(17) from Fausto A. C. Cariboni, Jul 16 2022
STATUS
approved