dihedral prime
(another Prime Pages' Glossary entries)
The Prime Glossary
Glossary: Prime Pages: Top 5000: A dihedral prime is a prime that remains prime when read on a 7-segment display (as seen on a digital clock or calculator) whether you hold it to a mirror, turn it upside down, or turn it upside down and hold it to a mirror. It must contain only the digits 0, 1, 2, 5, or 8. The sequence begins 2, 5, 11, 101, 181, 1181, 1811, ....

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