  Let a be a nonzero integer. If a is not congruent to 4 or 5 modulo 9 then
there is no Brauer-Manin obstruction to the existence of integers x, y, z such
that x^3+y^3+z^3=a. In addition, there is no Brauer-Manin obstruction to the
existence of integers x, y, z such that x^3+y^3+2z^3=a.
