second coefficient
In essence, this sum runs over all cycles of length 2 in the de Bruijn diagram. The
solution to the requirements by = xi and ax=yj is 
; however this notation must be understood to designate only as much of
the sequence as is needed. Thus 
could represent
0, 01, 010, 0101, and so on, but not 101, for example.
Harold V. McIntosh
E-mail:mcintosh@servidor.unam.mx