
REFERENCES

M. Gardner, "PoolBall Triangles", pp. 119120 and 128, Penrose Tiles to Trapdoor Ciphers, Freeman NY 1989.
M. Gardner, Puzzles From Other Worlds, Problem 8, pp. 143; 173, Random House NY 1984.
J. D. E. Konhauser et al., " Difference triangles", Problem 145, pp. 43; 1846, Which Way Did The Bicycle Go, MAA 1996.
P. Tougne, " Jeux Mathematiques", Aug. 1982 issue of Pour La Science (French edition of 'Scientific American'), Paris.


EXAMPLE

Illustrating the case of the unique example of n=5 with numbers 1 through 15:
6..14.15..3..13
..8..1..12.10
...7..11..2
....4...9
......5
For n=2 we have 1,3;2 and 2,3;1 so a(2) = 2.  Michael Somos, Apr 07 2012
