# [seqfan] Re: relation A033984 and A173138, solutions of mod n equations

Max Alekseyev maxale at gmail.com
Sun Feb 21 16:10:55 CET 2010

```I think that these sequences hit the difference between the binary
'mod' operation and the congruence 'mod' operation (we discussed some
other examples before).
As the latter is more general, I would suggest adopt this definition
in A033984, prepend currently missing element 4, and remove A173138.

Regards,
Max

On Sun, Feb 21, 2010 at 9:50 AM, Maximilian Hasler
<maximilian.hasler at gmail.com> wrote:
> I think the title of
> A173138
> Composite numbers n such that the congruence 2^(n-4)=1 (mod n) is solvable
>
> is not well chosen ( ... solvable -> solution to ... ?!)
>
> if n is odd, then 2^4 is invertible mod n so both equations are equivalent.
>
> and there can't be a solution > 4 to the 2nd equation (...=1)  for
> even n (which is explicitly excluded in A033984).
>
> M.H.
>
>
> On Sun, Feb 21, 2010 at 3:34 PM, Richard Mathar
> <mathar at strw.leidenuniv.nl> wrote:
>>
>> How are these two sequences related?
>>
>> http://research.att.com/~njas/sequences/?q=id:A173138|id:A033984
>>
>> 4,40369,673663,990409,1697609,2073127,6462649,7527199,7559479,14421169,21484129,37825753,57233047,
>>
>> 40369,673663,990409,1697609,2073127,6462649,7527199,7559479,14421169,21484129,37825753,57233047,130647919,141735559,179203369,188967289,218206489,259195009,264538057,277628449,330662479,398321239,501126487,
>>
>>
>>
>> _______________________________________________
>>
>> Seqfan Mailing list - http://list.seqfan.eu/
>>
>
>
> _______________________________________________
>
> Seqfan Mailing list - http://list.seqfan.eu/
>

```