[seqfan] [SeqFan] Re: sparse odd entries

Antti Karttunen antti.karttunen at gmail.com
Sat Apr 15 15:26:46 CEST 2017

In response to David Newman's Thu Apr 13 21:25:29 CEST 2017 posting
where he wrote:

> I'm looking for sequences which have few entries which are odd. A117958
which has a(n) congruent to 1 (mod 2) only for n=m squared, and m not
divisible by 3 is an example of what I'm looking for. Is there some easy
way to search for such sequences?

I reply that, for example, the following two grep commands piped together:
grep -v "[13579],.*[13579],.*[13579],.*[13579],.*[13579],.*[13579],.*[13579],"
stripped-2017-03-27 | grep "[13579],.*[13579],.*[13579],.*[13579],"

finds the entry A117958 among 22071 sequences (from stripped file
downloaded March 27 2017, see the Welcome-page for a recent version) in
whose data section there is at least four but no more than six odd terms.
So, additional selection criteria would be needed to prune the set to a
reasonable size (for human patience).

Best regards,


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