On Tuesday, May 14, 2013 2:31:23 PM UTC+1, Robin wrote: <snip>...etc. etc. etc,</snip>
Thanks very much for taking the time to reply.
The question comes from some work looking at generalising periodic Horadam sequences to a ring context and whether there is any much more interesting structure beyond just the ring you get by adjoining a couple of primitive roots of unity to Z.