## Multifactorial Primes of the form +/-2

Multifactorial numbers are of the form n!k

If k is even then n!k is odd for all odd n. Therefore n!k+/-1 are both even and hence not prime. In this case we can look for primes of the form n!k+/-2.  However as these numbers are not +/-1 from a number that can be easily factored Brillhart-Lehmer-Selfridge is not a suitable test to prove primality. So other than for the small primes I have used Marcel Martin's Primo which implements the elliptical curve primality proving (ECPP) algorithm  to prove numbers prime.

Certificates for Primo proofs are available on request.

 Type nmaxtested Digits of largest proven prime Digits of largest prp n is prime for: n!2+2 10000 5617 12896 primes n!2-2 10000 2914 16153 primes n!4+2 20000 2831 18109 primes n!4-2 20000 3918 18642 primes n!6-2 10000 1486 5113 primes n!10+2 26329 4031 10498 primes

Last Modified: 7th February 2012
Address questions about this web page to Ken Davis at "kraDenken(at)yahoo(dot)com(dot)au"