[seqfan] Re: Name for a type of set needed
M. F. Hasler
oeis at hasler.fr
Sat Mar 25 23:09:51 CET 2017
If you look at https://oeis.org/A284311/table you notice that there's an
error
in the data, leading to a value of 10 instead of 64.
IMHO it would be more natural to list the numbers with given prime factors
as rows, i.e., the transposed table, s.t. the first *column* would be
A005117 <https://oeis.org/A005117>,
in analogy with the similar oeis.org/A182944 <https://oeis.org/A182944> .
I don't know a name for the set of numbers which has a given squarefree
kernel (A007947), but one could simply say it's the inverse image
A007947^(-1) of that squarefree number.
Maximilian
On Fri, Mar 24, 2017 at 9:24 PM, Bob Selcoe <rselcoe at entouchonline.net>
wrote:
> Hi Seqfans,
>
> I just proposed sequence A284311, titled: "Array T(n,k) read by
> antidiagonals: T(1,k) = squarefree numbers > 1 in ascending order
> (A005117(k)); columns are non-squarefree numbers (in ascending order) with
> the exact same prime factors as T(1,k)".
>
> So for example, Column 6 is the set whose members have prime factors
> {2,5}: {10, 20, 40, 50, 80, 100, 160, 200...}.
>
> Is there a standard name for such sets?
>
> Cheers,
> Bob Selcoe
>
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