[seqfan] Re: Primes formed by concatenating other primes.
Maximilian Hasler
maximilian.hasler at gmail.com
Tue Mar 2 19:58:07 CET 2010
I agree with Franklin's observation.
Just to avoid confusion, the number "307" I added in the list should
be ignored (it is not wrong here), it originates from a glitch in my
PARI code for A019549 which allowed for "leading zeros"
(307 = 3 + 07).
(I already submitted the correction and the b-file requested by Eric.)
I hope this did not cause frustration to anyone...
M.H.
PS: to patch the PARI code, add "& n\10^(i-1)%10 &" before "return"
On Tue, Mar 2, 2010 at 7:42 PM, <franktaw at netscape.net> wrote:
> 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.
>>
>>
>>
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>>
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>>
>
>
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