Can a television series inspire a mathematical discovery? Apparently so.

In episode 73 of the popular comedy “The Big Bang Theory”, theoretical physicist Sheldon Cooper claims that 73 is the best number, the “Chuck Norris of numbers”

Not only is 73 a prime number. The product of its digits is 21 and this is precisely the position this number occupies in the sequence of prime numbers: 73, in fact, is the 21st prime number. It doesn’t end here. When we exchange the digits of 73, we still get a prime number, 37, which represents the 12th prime number. Have you noticed anything? Yes, 12 is the mirror number of 21 (i.e. obtained by reversing the numbers).

This did not escape the mathematician Chris Spicer , an avid and assiduous viewer of the famous television series who, along with his other two colleagues, asked himself this question: is 73 the only prime number to enjoy these properties?

Meanwhile, like good mathematicians, all three have provided a rigorous definition of “Sheldon prime” and accurately explain the “Sheldon conjecture”. A demonstration was published two months ago in the American Mathematical Monthly. It is, therefore, no longer conjecture but a theorem. Sheldon’s theorem.