[seqfan] Re: Primes formed by concatenating other primes.

[franktaw at netscape.net]

There are similar problems with A141033 - "Numbers that cannot be 
formed by the concatenation of previous terms".  The example shown of 
465 shows that concatenations of 3 or more terms are to be considered.  
Apparently the  intent is to disallow use of the same term twice in the 
concatenation.  But even so, 102 (for example) should not be there.

And no, the terms in the concatenation in A141409 need not remain in 
order; otherwise 73 would be in the sequence.  I'm not sure exactly 
what the intent was, but clearly the sequence contains errors.

Franklin T. Adams-Watters

-----Original Message-----
From: Maximilian Hasler <maximilian.hasler at gmail.com>

The sequence
A141409
         Prime numbers that cannot be formed by the concatenation of
previous terms.

    2, 3, 5, 7, 11, 13, 17, 19, 29, 31, 41, 43, 47, 59, 61, 67, 71, 79,
83, 89, 97, 101, 103, 107, 109, 127, 131, 139, 149, 151, 157, 163,
167, 179, 181, 191, 199, 227, 239, 251, 257, 263, 269, 277, 281, 293,
307, 349, 401, 409, 419, 421, 431, 439, 443, 449, 457, 461

has bad terms, e.g. [227, 257, 277, 293, 307, ...]

are in A019549 and thus should not be here.
(for 227 the question might be if the definition should read "...of
TWO previous terms",
but this does not explain 293 which is clearly wrong (AFAICS)
- or must the terms remain "in order", additionally ?)

M.



On Tue, Mar 2, 2010 at 6:49 PM, Eric Angelini <Eric.Angelini at kntv.be> 
wrote:
>
> Hello SeqFans,
> could someone send me please a zipped file with
> 10000 terms? I'm looking for something funny!
> http://www.research.att.com/~njas/sequences/A019549
> Best,
> É.
>
>
>
> _______________________________________________
>
> Seqfan Mailing list - http://list.seqfan.eu/
>


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