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| | Primality Proving 2.2: Fermat, probable-primality and pseudoprimes |
 | | Some early articles call all numbers satisfying this test pseudoprimes, but now the term pseudoprime is properly reserved for composite probable-primes. |
 | | There are 1,091,987,405 primes less than 25,000,000,000; but only 21,853 pseudoprimes base two [PSW80], so Henri Cohen joked that 2-PRP's are "industrial grade primes" [Pomerance84, p5]. |
 | | There may be relatively few pseudoprimes, but there are still infinitely many of them for every base a>1, so we need a tougher test. |
| primes.utm.edu /prove/prove2_2.html (461 words) |
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