In the September issue of Math Horizons, Jordan Ellenberg explains recent progress on the twin primes conjecture; Tommy Ratliff reports from the courtroom, where he finds pi on trial and an illegal prime number; and, in keeping with the Mathematics of Planet Earth 2013 theme, Glen Van Brummelen explores the nuances of finding the qibla, and George Heine explains just how we came to know that the Earth is not quite a perfect sphere. —Stephen Abbott and Bruce Torrence
Volume 21, Issue 1
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Important in its own right, a recent breakthrough by University of New Hampshire professor Tom Zhang represents a major step toward proving one of the most famous mathematical conjectures of all time.
To purchase the article from JSTOR: http://dx.doi.org/10.4169/mathhorizons.21.1.5
Paul K. Stockmeyer
Proportional division problems are more than 3,500 years old, but they continue to charm and challenge new generations of problem-solvers.
To purchase the article from JSTOR: http://dx.doi.org/10.4169/mathhorizons.21.1.8
Our student author reports on his transformative semester abroad in the city of Paul Erdős.
To purchase the article from JSTOR: http://dx.doi.org/10.4169/mathhorizons.21.1.12
Glen Van Brummelen
The widely practiced Muslim ritual of facing Mecca to pray turns out to involve the less widely practiced tools of spherical trigonometry.
To purchase the article from JSTOR: http://dx.doi.org/10.4169/mathhorizons.21.1.15
Is π a copyrightable fact? Can a prime number be illegal? Real court cases about real numbers can be real strange. (pdf)
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A recent math major exits the slow-moving traffic on Wall Street for the fast-paced world of digital advertising.
To purchase the article from JSTOR: http://dx.doi.org/10.4169/mathhorizons.21.1.20
Susan Goldstine, Sophie Sommer, and Ellie Baker
A decorative bracelet illustrating the seven-color theorem makes the four-color theorem seem plane boring.
To purchase the article from JSTOR: http://dx.doi.org/10.4169/mathhorizons.21.1.22
In the early 18th century, questions about the precise shape of the world sent mathematicians to the ends of the earth searching for an answer.
To purchase the article from JSTOR: http://dx.doi.org/10.4169/mathhorizons.21.1.25
The Math Horizons problem section, edited by Derek Smith and Gary Gordon
Did Euler’s choice of notation doom complex numbers to reside in an imaginary world?