For n = 7 a board with a(7) = 5 distinct distances is
+---+---+---+---+---+---+---+
7 | | | * | | | | |
+---+---+---+---+---+---+---+
6 | | | | | | * | |
+---+---+---+---+---+---+---+
5 | * | | | | | | |
+---+---+---+---+---+---+---+
4 | | | | * | | | |
+---+---+---+---+---+---+---+.
3 | | | | | | | * |
+---+---+---+---+---+---+---+
2 | | * | | | | | |
+---+---+---+---+---+---+---+
1 | | | | | * | | |
+---+---+---+---+---+---+---+
A B C D E F G
The distances between pairs of points are:
1) sqrt(10) (e.g., A5 to B2),
2) 2*sqrt(2) (e.g., A5 to C7),
3) 4*sqrt(2) (e.g., B2 to F6),
4) 2*sqrt(10) (e.g., A5 to G3), and
5) sqrt(26) (e.g., A5 to F6).
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