21701

This number is a prime.

The largest assigned 5-digit ZIP Code that is a Mersenne prime exponent. It belongs to Frederick, MD.

2⁹⁹⁹ + 21701 is prime.

M(21701) made international news when found by high school students Curt Landon Noll (now Landon Curt Noll) and Laura Nickel (now Ariel T. Glenn) using the California State University Cyber 174 on Halloween Eve in 1978. Note that Noll had previously developed a wide collection of "ASCII bats" (e.g., /\../\, /\oo/\, etc.) which have become part of his personal trademark.