# [seqfan] Re: A180268

Charles Greathouse charles.greathouse at case.edu
Mon Aug 23 22:23:04 CEST 2010

```Is there any reason to think this is an interesting sequence?
sigma(n) - n - 1 is Chowla's function (for n > 1), and the primality
of the Chowla function has some interest (it's A085842).  But what is
sigma(n) + 2n + 1 and why do we care if it's prime?  Is there any
relationship between the two?  They're primes at a distance of 3n + 2,
but that's not particularly interesting of itself.

Of course this comes back to the general, hard question of "what makes
a sequence interesting?".  The trouble is that if the sequence *is*
interesting, it doesn't make that apparent.

Charles Greathouse
Analyst/Programmer
Case Western Reserve University

On Mon, Aug 23, 2010 at 4:07 PM, Klaus Brockhaus
<klaus-brockhaus at t-online.de> wrote:
> %S A180268 988,1612,3172,5332,7852
> %N A180268 Numbers n with property that A000203(n)-n-1 is a prime number
> and 2*n+1-A000203(n) is a prime number.
>
> Utterly wrong or some additional condition is missing. I get
>
> 4, 10, 30, 42, 60, 70, 78, 102, 138, 186, 198, 216, 222, 228, 240, 246,
> 258,
> 270, 282, 360, 372, 390, 414, 438, 492, 498, 546, 582, 600, 606, 642,
> 708, 720,
> 756, 762, 774, 786, 810, 852, 870, 930, 942, 954, 988, 1002, 1014, 1020,
> 1026,
> 1038, 1068, 1086, 1182, 1266, 1290, 1314, 1362, 1368, 1386, 1398, 1470,
> 1542,
> 1584, 1612, 1626, 1638, 1656, 1680, 1686, 1698, 1710, 1722, 1740, 1794, 1836
>
> which is not in the OEIS.
>
> KB
>
>
>
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```