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Mathematics of Computation

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On the number of false witnesses for a composite number

Authors: Paul Erdős and Carl Pomerance
Journal: Math. Comp. 46 (1986), 259-279
MSC: Primary 11Y11; Secondary 11N56
MathSciNet review: 815848
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Abstract: If a is not a multiple of n and ${a^{n - 1}}\;\nequiv \;1\bmod n$, then n must be composite and a is called a "witness" for n. Let $F(n)$ denote the number of "false witnesses" for n, that is, the number of $a\bmod n$ with ${a^{n - 1}} \equiv 1\bmod n$. Considered here is the normal and average size of $F(n)$ for n composite. Also considered is the situation for the more stringent Euler and strong pseudoprime tests.

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Article copyright: © Copyright 1986 American Mathematical Society