# [seqfan] Re: Need help finding prime index values for sequence A363381

Thomas Young tomyoungmathman at gmail.com
Thu Aug 17 04:19:40 CEST 2023

```Thomas,

Thanks for your insights.  I'm not sure I agree but I don't  have a
counter-argument.  Does this take into consideration the n X n arrays such
as 1575 X 1575 = 3*3*5*5*7 X  3*3*5*5*7?  Given the number of odd factors,
there will be several f1 X f2 blocks that fill the array

Does anyone else have insights on this topic?

On Wed, Aug 16, 2023 at 6:25 AM Thomas Scheuerle <ts181 at mail.ru> wrote:

> Hello,
>
> I expect that it is already very difficult to find solutions for any odd n.
> Why ?
> I observed that most solutions can be found with some approach:
> If we then apply individual permutations inside rows and inside columns
> such that each
> of these permutations moves all elements the same absolute distance, then
> this approach can find solutions.
> If we investigate this case then we find that such permutations are
> generally even.
> That means they are a product of an even number of independent element
> swaps and can therefore only exist over
> an even number of elements.
> Therefore I conjecture if only solutions exist which can be reached by
> such permutations, then
> The only solutions for odd p in a p x p matrix will be rows or columns as
> shapes.
>
> Best regards
>
> Thomas
>

--
Tom Young
Executive Director
Minnesota State HS Math League

Math Teacher, Spring Lake Park HS, retired
763-568-0118
```