[seqfan] Re: Two "dumb" sequences and a question

Felix Fröhlich felix.froe at gmail.com
Wed Nov 30 19:28:33 CET 2022

Hi Ali,

my understanding is that the two sequences you propose are A053169 and

Best regards


Am Mi., 30. Nov. 2022 um 14:31 Uhr schrieb Ali Sada via SeqFan <
seqfan at list.seqfan.eu>:

> Hi everyone,
> Please consider the two sequences below:
> 1) Sequence AX contains all OEIS sequences where the A number is a term in
> the sequence itself. For example, A000027 since 27 is a positive integer.
> 2) Sequence AY contains all OEIS sequences where either:
> a) the A number is not a term in the sequence (e.g., A000040, since 40 is
> not a prime number),
> or
> b) we don’t know if the A number is a term in the sequence or not (e.g.,
> A329697).
> The question here is: Where should the number Y go? If we put it in
> sequence AY, then we know where it belongs and that contradicts the
> definition of AY.
> Also, it couldn’t be part of AX because Y is not a term of AY.
> I’m trying to have some basic understanding of set theory and I would
> really appreciate your feedback.
> Best,
> Ali
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