# [seqfan] Re: correcting A181539

Max Alekseyev maxale at gmail.com
Thu Nov 4 16:17:01 CET 2010

```Klaus,

According to your definition, a(2) must be equal 1. Why it is not?

Your terms from a(2) onward match those from my purported update to
A181539 that I sent to SeqFan earlier.

Regards,
Max

On Thu, Nov 4, 2010 at 2:39 AM, Klaus Brockhaus
<klaus-brockhaus at t-online.de> wrote:
>
>
> Sequence: A181539
> Sender: Klaus Brockhaus
> Date of submission: Nov 01 2010
>
> Description of changes, start:
> a(2) through a(4), a(7) through a(11) corrected, comment added, example replaced by
> Description of changes, end
>
>   %I A181539
> ! %S A181539 1,49,249,1249,18751,218751,781249,24218751,74218751,1425781249,
> ! %T A181539 13574218751,163574218751
>   %N A181539 a(n) = smallest number m such that m^2 == 1 mod 10^n.
> ! %C A181539 All terms have last digit 1 or 9. Squares of terms are 1, 2401, 62001, 1560001, 351600001, 47852000001, 610350000001, 586547900000001, 5508423000000001, 2032852170000000001, 184259414700000000001, 26756525040000000000001.
> ! %e A181539 1249^2 = 1560001 == 1 mod 10^4, and there is no smaller m such that m^2 == 1 mod 10^4. Hence a(4) = 1249.
>   %K A181539 more,nonn,new
>   %O A181539 1,2
>   %A A181539 Kevin Batista (kevin762401(AT)yahoo.com), Oct 29 2010
>
>
> Am 03.11.2010 16:51, schrieb N. J. A. Sloane:
>> I see that there are 2 different edited versions
>> of this sequence waiting to be processed, from
>> both Klaus and Bob (and possibly others).
>
>
>
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>

```