[tex]\displaystyle\\
\overset{15}{\underset{k=0}{\Sigma}} (3k-1) =-1 + 2 + 5 + 8 + \cdots + 44 =
\frac{16(44-1)}{2}=8\times 43 = 344 \\\\
\text{The general case:}\\\\
\overset{n}{\underset{k=0}{\Sigma}} (3k-1)=-1 + 2 + 5 + 8 + \cdots + (3n-1) = \frac{(n+1)((3n-1)-1)}{2}
[/tex]
