  A set of m distinct positive integers {a_{1},...a_{m}} is called a
Diophantine m-tuple if a_{i}a_{j}+n is a square for each 1\leqi<j\leqm . The
aim of this study is to show that some P_{k} sets can not be extendible to a
Diophantine quadruple when k=2 and k=-3 and also to give some properties about
P_{k} sets.
