Which cube members are not in the sequence and prove it?
2, 5, 8, 11, 14, ...
How can this be proved
Thus you want to find,Originally Posted by Natasha
$\displaystyle 3k+2=x^3$
I believe you may state that,
$\displaystyle x^3\equiv 1\mod 3$
if and only if, (there is a $\displaystyle k$ such as)
$\displaystyle 3k+2=x^3$.
Thus, all the values of $\displaystyle x$ which are
"cubic residues" which are $\displaystyle 1,4,7,10,13,...$
Maybe?