EN
A set of m positive integers with the property that the product of any two of them is the predecessor of a perfect square is called a Diophantine m-tuple. Much work has been done attempting to prove that there exist no Diophantine quintuples. In this paper we give stringent conditions that should be met by a putative Diophantine quintuple. Among others, we show that any Diophantine quintuple {a,b,c,d,e} with a < b < c < d < e$satisfies $d < 1.55·10^{72}$ and $b < 6.21·10^{35}$ when 4a < b, while for b < 4a one has either $c = a + b + 2√(ab+1) and $d < 1.96·10^{53}$ or c = (4ab+2)(a+b-2√(ab+1)) + 2a + 2b and $d < 1.22·10^{47}$. In any case, d < 9.5·b⁴.