Order 20: Marshall Hall Class 01 (this is as yet unchecked it comes from the
Paley matrix of order 20) 
---------01

 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
 1 1 1 1 1 1 1 1 1 1 - - - - - - - - - -
 1 1 1 1 1 - - - - - 1 1 1 1 1 - - - - -
 1 1 1 1 - 1 - - - - 1 - - - - 1 1 1 1 -
 1 1 1 - - - 1 1 - - - 1 1 - - 1 1 - - 1
 1 1 - 1 - - 1 - 1 - - - - 1 1 1 - 1 - 1
 1 1 - - 1 1 - - - 1 - 1 - 1 - 1 - - 1 1
 1 1 - - 1 - - - 1 1 1 - 1 - - - 1 1 - 1
 1 1 - - - 1 - 1 1 - - 1 1 - 1 - - 1 1 -
 1 1 - - - - 1 1 - 1 1 - - 1 1 - 1 - 1 -
 1 - 1 1 - - - 1 - 1 - - 1 1 - - - 1 1 1
 1 - 1 - 1 - 1 - 1 - - 1 - 1 - - 1 1 1 -
 1 - 1 - 1 - - 1 1 - 1 - - - 1 1 - - 1 1
 1 - 1 - - 1 1 - - 1 1 1 - - 1 - - 1 - 1
 1 - 1 - - 1 - - 1 1 - - 1 1 1 1 1 - - -
 1 - - 1 1 1 1 - - - - - 1 - 1 - 1 - 1 1
 1 - - 1 1 - - 1 - 1 - 1 - - 1 1 1 1 - -
 1 - - 1 - 1 - 1 1 - 1 1 - 1 - - 1 - - 1
 1 - - 1 - - 1 - 1 1 1 1 1 - - 1 - - 1 -
 1 - - - 1 1 1 1 - - 1 - 1 1 - 1 - 1 - -

 or

 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
 1-1 1-1-1 1 1 1 1-1 1-1 1-1-1-1-1 1 1-1
 1-1-1 1-1-1 1 1 1 1-1 1-1 1-1-1-1-1 1 1
 1 1-1-1 1-1-1 1 1 1 1-1 1-1 1-1-1-1-1 1
 1 1 1-1-1 1-1-1 1 1 1 1-1 1-1 1-1-1-1-1
 1-1 1 1-1-1 1-1-1 1 1 1 1-1 1-1 1-1-1-1
 1-1-1 1 1-1-1 1-1-1 1 1 1 1-1 1-1 1-1-1
 1-1-1-1 1 1-1-1 1-1-1 1 1 1 1-1 1-1 1-1
 1-1-1-1-1 1 1-1-1 1-1-1 1 1 1 1-1 1-1 1
 1 1-1-1-1-1 1 1-1-1 1-1-1 1 1 1 1-1 1-1
 1-1 1-1-1-1-1 1 1-1-1 1-1-1 1 1 1 1-1 1
 1 1-1 1-1-1-1-1 1 1-1-1 1-1-1 1 1 1 1-1
 1-1 1-1 1-1-1-1-1 1 1-1-1 1-1-1 1 1 1 1
 1 1-1 1-1 1-1-1-1-1 1 1-1-1 1-1-1 1 1 1
 1 1 1-1 1-1 1-1-1-1-1 1 1-1-1 1-1-1 1 1
 1 1 1 1-1 1-1 1-1-1-1-1 1 1-1-1 1-1-1 1
 1 1 1 1 1-1 1-1 1-1-1-1-1 1 1-1-1 1-1-1
 1-1 1 1 1 1-1 1-1 1-1-1-1-1 1 1-1-1 1-1
 1-1-1 1 1 1 1-1 1-1 1-1-1-1-1 1 1-1-1 1
 1 1-1-1 1 1 1 1-1 1-1 1-1-1-1-1 1 1-1-1

SNF: 1,2^9,10^{9},20
Quadratic Residues: 1 4 5 6 7 9 11 16 17