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Perfect numbers: Difference between revisions

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Fixed up LL method formula
m (→‎[[Perfect Numbers#ALGOL 68]]: (2ⁿ-1) × 2ⁿ ÷ 2)
m (Fixed up LL method formula)
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A number is perfect if the sum of its factors is equal to twice the number. An equivalent condition is that <tt>n</tt> is perfect if the sum of <tt>n</tt>'s factors that are less than <tt>n</tt> is equal to <tt>n</tt>.
 
Note: The faster [[Lucas-Lehmer_test]] is used to find primes of the form 2ⁿ-1, all ''known'' perfect numbers can derived from these primes using the formularformula (2<ttsup>(2ⁿn</sup> - 1) × 2ⁿ2<sup>n ÷- 21</ttsup>. It is not known if there are any odd perfect numbers.
 
=={{header|Ada}}==
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