Are all Almost Perfect Numbers Even?
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Open Question
It is known by Power of 2 is Almost Perfect that all powers of $2$ are almost perfect.
But it is not known whether there exist any odd almost perfect numbers. None have ever been found.
Sources
- 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $16$
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $16$