Try 2(power of n)-1 (where n=prime) results in a prime for a lot of ns. For example, 2 power of 3 =8 take away 1 =7 which is prime. A Mersenne prime. I thank you.
Snigger - just been looking at WIkipedia and there's even some things called McNugget primes - which stems from some historically thing about content of chicken McNugget boxes.
Comments
<prepares to stand corrected>
Correct, but late.
643
649?
They look awkward.
689?
691
Who said maths can't be fun eh? :oD
733