cyclic:= function(n,a)
local x, b, o ;
x:= [];
b:= 1;
o:= One(Integers mod n);
  if Gcd(n,a) = 1 then
    repeat
      b:= b*a mod (n);
      Add(x,b);
    until b=1;
  fi;
return x*o;
end;