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authorNorbert Preining <norbert@preining.info>2019-09-02 13:46:59 +0900
committerNorbert Preining <norbert@preining.info>2019-09-02 13:46:59 +0900
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+\input texinfo @c -*- TeXinfo -*-
+@setfilename perf-inf.inf
+@ifinfo
+ @paragraphindent 0
+@end ifinfo
+@iftex
+ @defaultparindent=0pt @parindent=0pt
+@end iftex
+
+@node Top, , (dir), (dir)
+@chapter Unsolved Problems
+@section Odd Perfect Numbers
+
+A number is said to be @i{perfect} if it is
+the sum of its divisors. For example, 6 is
+perfect because
+@tex $1+2+3 = 6$,
+@end tex
+@ifinfo
+1+2+3 = 6,
+@end ifinfo
+and 1, 2, and 3 are the only numbers that divide
+evenly into 6 (apart from 6 itself).
+
+It has been shown that all even perfect numbers
+have the form
+@tex $$2^{p-1}(2^{p}-1)$$ where $p$ and $2^{p}-1$
+@end tex
+@ifinfo
+@center 2^(p-1) (2^p - 1)
+
+where p and 2^p - 1
+@end ifinfo
+are both prime.
+
+The existence of @i{odd} perfect numbers is an
+open question.
+@bye