Question: In what month and year was the release of the novel that "The Divergent Series: Allegiant" was based on?

Context articles: The Divergent Series
Allegiant (novel)
Divergent trilogy
Divergent (film)
The Divergent Series: Allegiant
The Divergent Series: Insurgent
Ramanujan summation
Borel summation
Euler summation
List of Divergent characters

The Divergent Series is a feature film series based on the "Divergent" novels by the American author Veronica Roth.
 Distributed by Summit Entertainment and Lionsgate Films, the series consists of four science fiction films set in a dystopian society.
 They have been produced by Lucy Fisher, Pouya Shabazian, and Douglas Wick and star Shailene Woodley and Theo James as lead characters Beatrice Prior (Tris) and Tobias Eaton (Four), respectively.
 The supporting cast includes Ansel Elgort, Zoë Kravitz, and Miles Teller.
 The first film in the series was directed by Neil Burger, while the second and third films were directed by Robert Schwentke.
Allegiant is a science fiction novel for young adults, written by the American author Veronica Roth and published by HarperCollins in October 2013.
 It completes the "Divergent" trilogy that Roth started with her debut novel "Divergent" in 2011.
 The book is written from the perspective of both Beatrice (Tris) and Tobias (Four).
 Following the revelations of the previous novel, they journey past the city's boundaries to discover what lies beyond.
The "Divergent" trilogy is a series of young adult science fiction adventure novels by American novelist Veronica Roth set in a post-apocalyptic dystopian Chicago.
 The trilogy consists of "Divergent" (2011), "Insurgent" (2012) and "Allegiant" (2013).
 A related book, "Four", presents a series of short stories told from the perspective of one of the trilogy's characters.
Divergent is a 2014 American dystopian science fiction action film directed by Neil Burger, based on the novel of the same name by Veronica Roth.
 The film is the first installment in "The Divergent Series" and was produced by Lucy Fisher, Pouya Shabazian, and Douglas Wick, with a screenplay by Evan Daugherty and Vanessa Taylor.
 It stars Shailene Woodley, Theo James, Ashley Judd, Jai Courtney, Ray Stevenson, Zoë Kravitz, Miles Teller, Tony Goldwyn, Ansel Elgort, Maggie Q and Kate Winslet.
 The story takes place in a dystopian and post-apocalyptic Chicago where people are divided into distinct factions based on human virtues.
 Beatrice Prior is warned that she is Divergent and thus will never fit into any one of the factions.
 She soon learns that a sinister plot is brewing in the seemingly perfect society.
The Divergent Series: Allegiant is a 2016 American action adventure film directed by Robert Schwentke with a screenplay by Bill Collage, Adam Cooper, and Noah Oppenheim.
 It is the first of two cinematic parts based on the novel "Allegiant", the final book in the "Divergent" trilogy by Veronica Roth, and the third installment in "The Divergent Series".
The Divergent Series: Insurgent (also known simply as Insurgent) is a 2015 American science fiction action film directed by Robert Schwentke, based on "Insurgent", the second book in the "Divergent" trilogy by Veronica Roth.
 It is the sequel to the 2014 film "Divergent" and the second installment in "The Divergent Series", produced by Lucy Fisher, Pouya Shabazian and Douglas Wick, with a screenplay by Brian Duffield, Akiva Goldsman and Mark Bomback.
 Schwentke took over from Neil Burger as director, with Burger serving as the executive producer of the film.
 Along with the first film's returning cast, led by Shailene Woodley and Theo James, the sequel features supporting actors Octavia Spencer, Naomi Watts, Suki Waterhouse, Rosa Salazar, Daniel Dae Kim, Jonny Weston, Emjay Anthony, and Keiynan Lonsdale.
Ramanujan summation is a technique invented by the mathematician Srinivasa Ramanujan for assigning a value to divergent infinite series.
 Although the Ramanujan summation of a divergent series is not a sum in the traditional sense, it has properties which make it mathematically useful in the study of divergent infinite series, for which conventional summation is undefined.
In mathematics, Borel summation is a summation method for divergent series, introduced by .
 It is particularly useful for summing divergent asymptotic series, and in some sense gives the best possible sum for such series.
 There are several variations of this method that are also called Borel summation, and a generalization of it called Mittag-Leffler summation.
In the mathematics of convergent and divergent series, Euler summation is a summability method.
 That is, it is a method for assigning a value to a series, different from the conventional method of taking limits of partial sums.
 Given a series ∑"a", if its Euler transform converges to a sum, then that sum is called the Euler sum of the original series.
 As well as being used to define values for divergent series, Euler summation can be used to speed the convergence of series.
This is a list of major and minor characters in the "Divergent" book trilogy and its subsequent film adaptation, "The Divergent Series".