On the television show The Big Bang Theory, physicist Sheldon Cooper claimed that 73 is the best number. In the November issue of Math Horizons Jessie Byrnes, Chris Spicer, and Alyssa Turnquist investigate Sheldon's claim and leave the mathematical community with a new conjecture about prime numbers. Brian Lins explains how he used mathematics to make his car pool both easy to manage and fair to all drivers. Students: Are you interested in doing mathematics this summer? We've got some ideas for you: five students write about their summer mathematical adventures. Our Do the Math! series continues with Laszlo Bardos presenting several ways to make a torus out of paper. Enjoy these articles and more in this issue of Math Horizons. —Dave Richeson
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A Toast! To Type 15!
Three researchers discover a new pentagonal tiling of the plane.
Making a Hash of Things
Adam A. Smith and Ursula Whitcher
Use a hash function to protect stored passwords.
The Sheldon Conjecture
Jessie Byrnes, Chris Spicer, and Alyssa Turnquist
In The Big Bang Theory, Sheldon asserts that 73 is the best number.
Whose Turn Is It to Drive Today?
Brian Lins describes a fair and convenient method of managing a car pool.
Make Math Your Summer Fling
Alissa S. Crans and Beck Weinhold
Five students describe their mathematical summers.
Do The Math!
How to Make a Torus
Laszlo C. Bardos shows various ways of making a torus out of paper. (pdf)
Constructing the Miyaoto-Moneroa-Monterde model of a torus: printable template and video instructions.
Constructing a paper torus with seams along Villarceau circles: printable template and video instructions.
Theron J. Hitchman reviews Things to Make and Do in the Fourth Dimension, by Matt Parker;
Heather Moon reviews Single Digits, by Marc Chamberland.
10 Life Lessons from Differential Equations
John D. Cook
What can we learn about life from the study of differential equations?
The Power of Two . . . in Poetry?
Amy Shell-Gellasch and J. B. Thoo describe the mathematics in Indian poetry.
The Math Horizons problem section, edited by Gary Gordon
Aftermath: The Common Core for Mathematics in a Nutshell
Eve Torrence argues that we can get students hooked on mathematics using art.