What does "the sum of every third element in the $n$-th row of Pascal's triangle" mean? I am looking at the following problem. I don't want to know how it's done,  I would just like to see the problem reworded in less confusing terms if possible:


Let ${n\choose k}$ be the $k^{th}$ entry of the $n^{th}$ row of the triangle.  (starting at $k=0$)
$S_{n,0} = {n\choose 0}+{n\choose 3}+{n\choose 6}+\cdots\\
S_{n,1} = {n\choose 1}+{n\choose 4}+{n\choose 7}+\cdots\\
S_{n,2} = {n\choose 2}+{n\choose 5}+{n\choose 8}+\cdots$
