# [seqfan] Re: A187871

Peter Pein petsie at dordos.net
Wed Mar 16 18:01:42 CET 2011

```Am 15.03.2011 18:12, schrieb Alexander P-sky:
> Re: A187871
>
>> Meller's term, 11032567498, is smaller than your 12347658910
> Though it is obvious, perhaps it is worth to add to the definition that
> a(n+1) is the minimal integer number, which complies with the condition
> a(n+1)>  a(n)
>
> On 3/15/11, N. J. A. Sloane<njas at research.att.com>  wrote:
>> Peter, I admit I made a mistake in my definition of A187871.
>> Here is a corrected version  (in the internal format):
>>
>> %I
>> %S 1,12,123,1234,14325,143256,1234765,12347658,123476589,11032567498
>> %N a(1)=1; for n>  1, a(n) is the smallest number that is formed by
>> arranging the decimal numbers "1", "2", ..., "n" in some order so that the
>> sum of every pair of adjacent numbers "i" "j" is prime.
>> %C A051237 and A187869 are the sequence that result if in addition we
>> require that the number begins with "1" and ends with "n".
>> %H Claudio Meller,<a
>> href="http://www.misacertijos.com.ar/2011/03/lineas-con-numeros-de-1-n.html">Lineas
>> con numeros de 1 a n</a>.
>> %Y Cf. A051237, A187869.
>> %K nonn,base,more,changed
>> %O 1,2
>> %A N. J. A. Sloane (njas(AT)research.att.com), Mar 14 2011
>> %E a(6) to a(10) from Claudio Meller, Mar 14 2011
>>
>> You sent a b-file for this. You version begins:
>>
>> 1,12,123,1234,14325,143256,1234765,12347658,123476589,12347658910,1234710985611,
> 123476512118910,12347651211891013,1234761310981112514,123476512118151491013,
> 12347651211891013161514,1234765891013161514171211,123476589101316151417121118
>> The difference is in the 10th term. Meller's term, 11032567498, is smaller
>> than your 12347658910, so yours is a different sequence. Can you tell
>> me exactly how you defined your version?
Well, the second "digit" in 11032567498 is "10" and as 10 is greater
than 2 my Mma-program tried "2" before "10" and came to a result. The
alternative would be to calculate all 'pairwise-prime-sum-sequences' and
to compare the strings interpreted as numbers. That would last a long
time for a(100) :-(

```