[seqfan] Re: (3^n+1)/2 is prime, A171381
guninski at guninski.com
Tue Jun 15 19:06:35 CEST 2010
On Mon, Jun 14, 2010 at 04:31:56PM -0400, Max Alekseyev wrote:
> Btw, the exponent 20 is listed there as (primality) "character unknown".
> So, the claim that (3^(2^20)+1)/2 is not a prime should probably be
> submitted to reflect an updated status of the exponent 20.
According to PFGW, 2^20 is really not in the sequence (less than an hour):
PFGW Version 126.96.36.19900405.x86_Stable [GWNUM 25.14]
(3^1048576+1)/2 is composite: RES64: [9EE4CA1AABB9A816] (3229.8733s+0.0424s)
Base 5. Base 3 is ugly for this thread.
According to prognosis of prime hunting pros at:
2^22 will take "a couple of days" (well not with gp/pari).
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