What is a dihedral prime number?

It's true, there are several prime numbers that, if you read them upside down in a seven-segment display on a calculator, or if you reflect them in a mirror, are still prime numbers. Examples: 2, 5, 11, 101, 181, 1181, 1811, 18181

More Info: en.wikipedia.org

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37 Comments

Player

Never heard of them. Like most math questions that appear here.

Eve

Didn't know, don't care, I'm done with math in this lifetime, lol

brezza marina

Not well explained for the non math savvies that want to learn.

Phil Kennelty

That definition would include if the number were sideways or at a 45 degree angle or any other angle and therefor is not true exept for 0 which is not a prime number by definition.