How many perfect odd numbers exist?
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It is unknown
It is unknown whether there is any odd perfect number, though various results have been obtained. In 1496, Jacques Lefèvre stated that Euclid's rule gives all perfect numbers,[18] thus implying that no odd perfect number exists. Euler stated: "Whether (...) there are any odd perfect numbers is a most difficult question". More recently, Carl Pomerance has presented a heuristic argument suggesting that indeed no odd perfect number should exist. All perfect numbers are also Ore's harmonic numbers, and it has been conjectured as well that there are no odd Ore's harmonic numbers other than 1.
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Answers by country
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1
2
It is unknown
answers
the Netherlands
14
France
10
Republic of Ireland
13
Australia
18
India
52
Germany
376
Poland
2560
Austria
73
the United States
65
Switzerland
40
Greece
10
the United Kingdom
69
Spain
11
Canada
11