Hexagonal Numbers as Relay Question
Relay questions can come in many forms. They typically start with let T = TNYWR (The Number You Will Receive). The idea is you can do a lot of work on solving the problem before you know what T is. Then when you receive T from a teammate, you can finish up your problem and get your answer.
Relays appear on mathleague.org High School competitions and on ARML, www.arml.com, competitions.
This particular question is explained at http://www.math-magic.com/misc/hexagonal.htm