<|system|>
Calculate the sum $1 + 3 + 5 + \cdots + 15 + 17$.</s>.
<|user|>
Can you answer based on context?
<|assistant|>
I notice that this is an arithmetic series, where each term is 2 more than the previous term. I also notice that there are 9 terms in the series, since the first term is 1 and the last term is 17, and I can divide the difference by 2 and add 1 to get the number of terms. To find the sum of an arithmetic series, I can use the formula $S_n = \frac{n}{2}(a_1 + a_n)$, where $S_n$ is the sum of the first $n$ terms, $a_1$ is the first term, and $a_n$ is the nth term. In this case, $n = 9$, $a_1 = 1$, and $a_n = 17$. Plugging these values into the formula, I get $S_9 = \frac{9}{2}(1 + 17) = \frac{9}{2}(18) = 81$. 