  A well-known open problem is to show that the cubic form $x^3+y^3+2z^3$
represents all integers. An obvious variant of this problem is whether every
integer can be {\em primitively} represented by $x^3+y^3+2z^3$. In other words,
given an integer $n$, are there coprime integers $x$, $y$, $z$ such that
$x^3+y^3+2z^3=n$? In this note we answer this variant question negatively.
Indeed, we use cubic reciprocity to show that for every integral solution to
$x^3+y^3+2z^3=8^m$,the unknowns $x$, $y$, $z$ are divisible by $2^m$.
