AND 
WITH APPLICATIONS TO 
OF A FIELD![Sample our Mathematics & Statistics journals, sign in here to start your FREE access for 14 days]({"type":"image" , "src" : "/sda/5943/TOC-Subject-Sample-2021-Mathematics-Statistics.jpg"})
ABSTRACT
Through determining all the solutions of
and
in
and of
and
in
we have proved that i)
is a subgroup of
iff
, ii)
is a subgroup of
iff
iii) If
then
is a subgroup of
iff n=2 and
which partially confirms a conjecture on
posed by Browkin in Citation[1].
ACKNOWLEDGMENT
We should like to express our thanks to professor Tong Wenting for his guidance and help. Supported by the NSFC Grant and the National Distinguished Youth Science Foundation of China Grant.