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← Season 1 Person of InterestSeason 2 (Flashbacks in parentheses) Season 3 →
201The Contingency” (Finch) 209C.O.D. 217Proteus
202Bad Code” (Root) 210Shadow Box 218All In
203Masquerade 2112πR 219Trojan Horse
204Triggerman 212Prisoner's Dilemma” (Reese) 220In Extremis” (Fusco)
205Bury the Lede 213Dead Reckoning” (Stanton) 221Zero Day” (Finch/Ingram)
206The High Road” (Finch) 214One Percent” (Finch/Ingram) 222God Mode” (Finch/Hersh)
207Critical 215Booked Solid
208Til Death” (Finch) 216Relevance

POI 0211 Main.png



Air dateJanuary 3, 2013

Running time43:45

Production code2J7211

Written byDan Dietz

Directed byRichard J. Lewis


ID(s) from IntroID.030/2021.01

Images (33)

Pi: The ratio of the circumference of a circle to its diameter, and this is just the beginning. It keeps on going, forever, without ever repeating.

— Finch

"2πR" is the 11th episode of season 2, and the 34th produced hour of Person of Interest. It originally aired on January 3, 2013.


Finch goes undercover as a high school substitute teacher to protect a teen genius POI as Carter undertakes a dangerous mission to stop the FBI from determining that an imprisoned Reese is the "Man In a Suit."

Origin of the Title

The episode's title is a reference to pi (π), the ratio of the circumference of a circle to its diameter. Pi is a transcendental number. As such, its decimal representation is considered to be unending and has been calculated to over 10 trillion digits. The circumference of a circle is calculated by 2πR, and the Caleb Phipps story in this episode goes full circle, starting and ending with death in a subway station.

Main Plot Points

  • The FBI and Nicholas Donnelly's investigation of the man in the suit continues.
  • Carter and Finch try to hide Reese's identity.
  • Carter removes Reese's fingerprints from the NYPD database and switches out his DNA sample.
  • Carter is forced to interrogate Reese.

Episode Notes

  • Finch uses the infinite value of pi as a metaphor for infinite possibility open to each student, depending upon what they choose to do with that knowledge. 
  • Chris Beckner, the computer science teacher, describes ARPANET, the first computer network, to his students. Advanced Research Projects Agency Network (ARPANET) was funded by the U.S. Department of Defense to connect universities and research laboratories engaged in defense-related projects. After several attempts to link various nodes, ARPANET went online in 1969 with a transmission from the University of California, Los Angeles to three other sites [Stanford Research Institute's Augmentation Research Center, the University of California, Santa Barbara and the University of Utah]. Although ARPANET was shut down in 1990 [formally decommissioned February 28, 1990], it is widely regarded as the birthplace of the modern internet.
  • Finch is appalled by the idea that mathematics is used as punishment. From a pedagogical point of view, he has reason to be appalled; it is well established in the field of education that using academic skills as punishment, such as when teachers have children write sentences or do pointless calculations, has little effect on behavior, but increases a student's dislike of the subject matter.
  • The school principal chastises Finch for telling the students to find a way around the calculation assigned as a punishment. However the formula that quickly solves the problem was found by mathematician Carl Friedrich Gauss at school after his professor had given his class the same problem as punishment.
  • A picture of Carl Friedrich Gauss, the German mathematician Finch discusses, is hanging at the upper left hand corner of the classroom. Gauss's work influenced numerous fields of mathematics, including number theory, algebra and statistics.
  • The remark of Finch to Caleb about a paper note with some code in it that he had dropped saying that to do multi-threading he'll have to use atomic variables is a concept in computer science about concurrent processes and parallel programming in which operations are atomic or indivisible, meaning not further decomposed or interrupted before success or failure (including timeouts, possessing safeguard backtracking mechanisms to restore the original value in case of error) is accomplished assuring consistency in the data.

Production Notes

  • This episode was originally titled "Above Average."

Bloopers and Continuity Errors

  • On his first day as a teacher, Finch writes his name Mr. Swift on the blackboard. When he turns around, the letters have changed shape, indicating another take or possibly another production day.
  • Finch's claim that because pi is non-repeating and non-terminating, "contained within this string of decimals [pi as a decimal number] is every single other number" is a non-sequitur.
  • Compressing the Library of Congress (shown as 235 TB) onto an ordinary thumb drive (e.g. 64GB) would require a compression rate of under 0.03%. For such diverse source material, this is currently thought to be impossible, particularly since the decompression happened in mere seconds.


2x11 - continuity.png



  • "How'd I know the federal government would be no match for you?" (Reese to Finch)