Hi! Jean Penne has written about 3^n-2. I've played for a while with 5^n-(5-1)^5=5^n-1024. Of course, for n=5k they are composite; since 4=2^2 they are also composite for even n. Moreover, there are some series of composite numbers, e.g. for n=10,16,22,28,... they are divisible by 7 (it can be proven), and for n=3k d=31 is a divisor (I had no time to prove it, but it is easy, I think). These rules excludes many of numbers, so for n<1000 I've found only three primes: 5^7-1024=77101, 5^11-1024=48827101 and 634-digit one for n=907 (primality tested by Marcel Martin's Primo.
Regards Wojtek (WsF) =============================================== Wojciech Florek (WsF) Adam Mickiewicz University, Faculty of Physics ul. Umultowska 85, 61-614 Poznan, Poland phone: (++48-61) 8295033 fax: (++48-61) 8295167 email: [EMAIL PROTECTED] _________________________________________________________________________ Unsubscribe & list info -- http://www.ndatech.com/mersenne/signup.htm Mersenne Prime FAQ -- http://www.tasam.com/~lrwiman/FAQ-mers
