  We show that for a large class of cubic polynomials $f$, every sufficiently
large number can be written as a sum of seven positive values of $f$. As a
special case, we show that every number greater than $e^{10^7}$ is a sum of
seven positive octahedral numbers, where an octahedral number is a number of
the form $\frac{2x^3+x}{3}$, reducing an open problem due to Pollock to a
finite computation.
