%N Orders of Parker rings.
%C A field or ring is called "Parker" if no 3 X 3 magic square of 9 distinct squared elements can be formed. Conjecture: the sequence is complete.
%C Example: the fact that p=31 is listed is taken to mean one cannot construct a 3 X 3 magic square of distinct squared elements of the ring of order 31.
%H Onno M. Cain, <a href="https://github.com/onnomc/parker-ring-search">parker-ring-search SageMath code</a>, Apr 24, 2019.
%H Onno M. Cain, <a href="https://arxiv.org/abs/1908.03236">Gaussian Integers, Rings, Finite Fields and the Magic Square of Squares</a>, arXiv:1908.03236 [math.RA], 2019.
%H Matt Parker & Brady Haran, <a href="https://www.youtube.com/watch?v=aOT_bG-vWyg">The Parker Square</a>, Numberphile video (2016).
%Y Cf. A308838 (for finite field).
%A _Michel Marcus_, Aug 18 2019