Problem:
Consider the arithmetic sequence defined by $a_1=-\frac{72}{65}$, and $a_n=a_{n-1}+-4$ for $n > 1$. Compute the nth partial sum, $S_n=\sum_{k=1}^n a_k$, where $n=12$.
Answer:
$-\frac{18024}{65}$
{'source': 'AMPS', 'file': 'amps/mathematica/algebra/arithmetic_series/15395.txt'}