Editing Fermat primality test (section)

== Example ==
Suppose we wish to determine whether ''n''&nbsp;=&nbsp;221 is prime. Randomly pick 1 < ''a'' < 220, say ''a''&nbsp;=&nbsp;38. We check the above congruence and find that it holds:
:<math>a^{n-1} = 38^{220} \equiv 1 \pmod{221}.</math>
Either 221 is prime, or 38 is a Fermat liar, so we take another ''a'', say 24:
:<math>a^{n-1} = 24^{220} \equiv 81 \not\equiv 1 \pmod{221}.</math>
So 221 is composite and 38 was indeed a Fermat liar. Furthermore, 24 is a Fermat witness for the compositeness of 221.