[seqfan] Re: Primes with strokes (blog)

[Éric Angelini]

Last update on the topic on my personal blog:
https://bit.ly/2s1L5No
Best,
É.


> Le 22 novembre 2019 à 12:27, Éric Angelini <eric.angelini at skynet.be> a écrit :
> 
> 
> David S. just wrote to me about S.
> Here is my answer.
> ------------------
> Hello David,
> thanks for your comments,
> well this seq is easy to start by hand
> as we lexicographically care about S,
> not the primes!
> 
> > concatenated digits between two strokes is prime."
> S = 1,3,2,4,7,5,6,8,9,10,11,14,16,18,83,13,17
> 
> a(1)=1 is ok
> a(2) cannot be 2 as 2 is a prime digit
> and if we strike it is not ok: 12 is a
> composite. We then try a(2)=3 and
> it works as 13 is prime.
> a(3)=2 is ok too as 2 is a prime between 
> two strokes
> a(4)=4 is the smallest available integer
> not leading to an immediate contradiction 
> a(5) cannot be 5 as a stroke after 5
> would produce the composite 45. But
> a(5)=6 is ok -- as 6 is the smallest 
> available integer not leading to an 
> immediate contradiction; so my seq 
> is wrong. Back to the blackboard!
> Thanks for your sharp eye, David!
> (going now for a lunch -- will fix this
> later this afternoon)...
> Best,
> É.
> 
> 
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