## pseudoprime

**pseudoprime** /n./ A backgammon prime (six consecutive occupied
points) with one point missing. This term is an esoteric pun
derived from a mathematical method that, rather than determining
precisely whether a number is prime (has no divisors), uses a
statistical technique to decide whether the number is `probably'
prime. A number that passes this test was, before about 1985,
called a `pseudoprime' (the terminology used by number theorists
has since changed slightly; pre-1985 pseudoprimes are now
`probable primes' and `pseudoprime' has a more restricted meaning
in modular arithmetic). The hacker backgammon usage stemmed from
the idea that a pseudoprime is almost as good as a prime: it does
the job of a prime until proven otherwise, and that probably won't
happen.

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