Another way of looking at this is to visualize $\int_0^\infty c\,dx$, where $c>0$. Now make a drawing, including the $x$-axis, of what this integral...
Conceptually an integral corresponds to the area under a graph.
If that graph extends to infinity, the height of the graph must approach zero, since...
Erm... then I'm not quite sure what I can use or not.
Can you perhaps use the fact that a series $x_1 + x_2 + ...$ can only converge if $x_n \to 0$?...
Each term in the series can be represented by $5+9n,\,0\le n\le240$. In order for a term to be divisible by $5$, $n$ must be divisible by $5$. Hence...
Sometimes editing a thread title is an issue, but the issue is with vBulletin. If you ever want to change a thread title, and can't, just let me know...