upside down
(another Prime Pages' Glossary entries)
The Prime Glossary
Glossary: Prime Pages: Top 5000: "Turning a number upside down" refers to the process of inverting a number's decimal representation by rotating it 180o (see the counter-clockwise example below).
A Number Turned Upside Down

See Also: Strobogrammatic, Tetradic, TriadicPrime

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