Each week, we post a new Challenge Problem for you to attempt. If you submit the correct answer, you will be entered into that week’s drawing for two free Manhattan Prep GRE Strategy Guides.

The sequence of numbers

a_{1},a_{2},a_{3}, …,a_{n}, … is defined by for each integernâ‰¥ 1.Quantity A

The sum of the first 20 terms of this sequenceQuantity B

The sum of the first 19 terms of this sequence

See the answer choices and submit your pick over on our Challenge Problem page.