Proper Factor
A proper factor of a positive integer 
is a factor
of 
other than 1 or 
(Derbyshire 2004,
p. 32). For example, 2 and 3 are positive proper factors of 6, but 1 and 6 are
not.
Compare with the term proper divisor, which means a factor of 
other than 
(but including
1).
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