[seqfan] Re: A061421

[Georgi Guninski]

On Sun, Dec 02, 2012 at 08:35:57PM +0400, юрий герасимов wrote:
> 
> Dear SegFans, If A061421  Primes of the form 2^n + n + 1 : 2, 7, 71, 110427941548649020598956093796432407239217743554726184882600387580788973,
> a(5) = 2^1884 + 1884 + 1,.., these
> A_____?   Primes of the form 4^n - n - 1 : 2, 13, 251, 4294967279, a(5) = ?
> Regards, Juri-Stepan Gerasimov.
>

For computations like this, OpenPFGW is your friend:

$egrep 'PRP|prime' /tmp/pri1.log 
4^1-1-1 is trivially prime!: 2
4^2-2-1 is trivially prime!: 13
4^4-4-1 is trivially prime!: 251
4^16-16-1 is trivially prime!: 4294967279
4^944-944-1 is 3-PRP! (0.0039s+0.0942s)
4^33478-33478-1 is 3-PRP! (8.5771s+1.3188s)


According to pari n=944 is pseudoprime.