# [seqfan] Re: successive powers of 2 modulo n

Alonso Del Arte alonso.delarte at gmail.com
Sat Jun 11 04:16:49 CEST 2011

```My point still stands that p – 1 is not infinity. And, as David has probably
figured out by now, since we're dealing with 2^n, then each value is always
followed by the same value each time it occurs.

E.g., mod 197, 2 is always followed by 4, and 4 is always followed by 8, and
8 is always followed by 16, etc., and it gets a little more interesting when
we get to 128, but eventually we'll get back to 2 which will be followed by
4 again.

Al

On Fri, Jun 10, 2011 at 6:20 PM, <franktaw at netscape.net> wrote:

> No, you can't. If 2 is a primitive root of p, then all p-1 values do occur.
>
> Franklin T. Adams-Watters
>
>
> -----Original Message-----
> From: Alonso Del Arte <alonso.delarte at gmail.com>
>
> Even a very large prime is still finite. Let's say p is a titanic prime.
> There are only (p – 1) possibilities for 2^n mod p. Using Fermat's "little"
> theorem you can probably reduce this further still.
> ...
>
>
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>

```

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