[seqfan] Re: when is 1234...n a prime?

[Sean A. Irvine]

rSm(82) = 8281...4321 is known to be prime.

http://www.gallup.unm.edu/~smarandache/s-number.htm

Sean.

On 12 October 2015 at 15:28, Marc LeBrun <mlb at well.com> wrote:
> I'm idly curious, but lack the gumption to calculate:
>
> What happens if you append on the left?
> 1 21 321 4321 54321 ... 10987654321 1110987654321 121110987654321 ...
>
> What happens if you reflect the numbers?
>
> 123456789101112 --> 211101987654321
>
> 121110987654321 --> 123456789011121
>
> What's the least N for which all four are prime?
>
>
>
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