Pair correlation for fractional parts of αn2

It was proved by Weyl [8] in 1916 that the sequence of values of αn2 is uniformly distributed modulo 1, for any fixed real irrational α. Indeed this result covered sequences nd for any fixed positive integer exponent d. However Weyl's work leaves open a number of questions concerning the finer distribution of these sequences. It has been conjectured by Rudnick, Sarnak and Zaharescu [6] that the fractional parts of αn2 will have a Poisson distribution provided firstly that is Diophantine, and secondly that if a/q is any convergent to then the square-free part of q is q1+o(1). Here one says that is Diophantine if one has |α-a/q|≫ εq-2-ε for every rational number a/q and any fixed ε > 0. In particular every real irrational algebraic number is Diophantine. One would predict that there are Diophantine numbers for which the sequence of convergents pn/qn contains infinitely many squares amongst the qn. If true, this would show that the second condition is independent of the first. Indeed one would expect to find such with bounded partial quotients. © 2010 Cambridge Philosophical Society.