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Factoring numbers mentally

  1. Sep 26, 2008 #1
    Does anybody have any good tricks to quickly factor a number in your head, or a trick that can be done quickly on paper? The best method that I know without using a calculator is the traditional method of finding two not-necessarily-prime factors and factoring those with the same method.
  2. jcsd
  3. Sep 27, 2008 #2
    Google "divisibility rules" or "divisibility tests" . However, mental calculations are generally restricted to working with small numbers and are not generally useful in serious number theory problems, and I don't see any advantage to excluding the use of a calculator.
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