When Harold Finch (Michael Emerson) hacked Caleb Phipps' (Luke Kleintank) school records, one of them included a "bubble test" in which he filled in the bubbles to say, "Waste of time".
Harold pulls Caleb's paper out of the trash can, which contains Gauss' complete solution and the answer to the assigned problem:
(100+1) x 100 / 2 = 5,050. Pairwise, from beginning to end, every combination equals 101 and there are 50 pairs.
The episode's title "2 pi r" is the formula used to find the circumference of a circle.
The working title for this episode was "Above Average."