Abstract: Let n be an integer. A set of positive integers {a_1, a_2,...,a_m} is said to have the property of Diophantus of order n, symbolically D(n), if a_i*a_j + n is a perfect square for all 1<=i<j<=m. It is known that for any integer l and any set {a, b} with the property D(l^2), where ab is not a perfect square, there exist an infinite number of sets of the form {a, b, c, d} with the property D(l^2). Using this result, we construct such sets with elements given in terms of Pell and Pell-Lucas...

Published in 1998.