A dihedral prime is a prime number 
such that the "LED representation" of 
(i.e., the arrangement of horizontal and vertical lines seen
on a digital clock or pocket calculator), 
upside down, 
in a mirror, and 
upside-down-and-in-a-mirror are all primes.
The decimal digits of 
are therefore restricted to 0, 1, 2, 5, and 8. The first few
dihedral primes are 2, 5, 11, 101, 181, 1181, 1811, 18181, 108881, 110881, 118081,
120121, ... (OEIS A134996).
Dihedral Prime
See also
Tetradic NumberExplore with Wolfram|Alpha
References
Rivera, C. "Problems & Puzzles: Puzzle 039-The Mirrorable Numbers (by Mike Keith)." https://www.primepuzzles.net/puzzles/puzz_039.htm.Sloane, N. J. A. Sequence A134996 in "The On-Line Encyclopedia of Integer Sequences."Referenced on Wolfram|Alpha
Dihedral PrimeCite this as:
Weisstein, Eric W. "Dihedral Prime." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/DihedralPrime.html