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I caught a very brief back-and-forth on Twitter the other day—actually, Amazon's "Prime Day," July 15—wherein mathematician author Jordan Ellenberg jokingly wondered why it was called "Prime Day" when 15 wasn't a prime.

One of the replies suggested that it was "Grothendieck Prime" Day, which led me to this:

The number 57 is sometimes called a "Grothendieck prime", after the prodigious mathematician Alexandre Grothendieck who is alleged to have said 57 when asked to give an example of a specific prime.

Which also reminded me of this in an interview with Stephen Colbert and Terence Tao, where Tao ever so briefly begins to suggest that 27 is prime (at around 2:50 where he talks a bit about twin primes).

And 27 certainly has a little "priminess" to it. Not as much as 57 I would say, mostly because 27 is featured as a product in a "basic multiplication fact," but I get it. So maybe "Colbert Prime" for 27. "Tao Prime" might be too confusing, even for mathematicians.