Re: Calculating powmod...

[Walter Neumann <neumann@math.columbia.edu>]

Do

Mod(2, 9182347891541)^9182347891540

On Sun, 18 Oct 2009, David Cleaver wrote:

> Hello,
>
> I'm interested in calculating "powmod"'s such as:
>
> However, when I ran the function, it gave an error:
> ***   length (lg) overflow
>
> Actually, I'm really interested to see if a number is a base 2 pseudoprime. 
> I saw the ispseudoprime function, but that uses the strong test, and I just 
> need to know:
> 2^(n-1) == 1 (mod n)
>
> I'm only going to be working with 64-bit inputs.  Is there some setting I 
> need to change in pari to be able to find out the above?  Or is there some 
> function I might have overlooked that performs that calculation?  Thanks for 
> your time.
>
> -David C.