pseudoprime

( n.)

   A  backgammon  prime (six consecutive occupied points) with one point
   missing.  This  term is an esoteric pun derived from number theory: a
   number that passes a certain kind of "primality test" may be called a
   pseudoprime  (all primes pass any such test, but so do some composite
   numbers),  and  any  number  that  passes  several is, in some sense,
   almost  certainly  prime.  The hacker backgammon usage stems from the
   idea  that a pseudoprime is almost as good as a prime: it will do the
   same job unless you are unlucky.

[glossary]
[Reference(s) to this entry by made by: {backgammon}]