# [seqfan] Re: correcting A181539

RGWv rgwv at rgwv.com
Thu Nov 4 07:02:41 CET 2010

```?%I A181539
%S A181539
1,51,751,8751,18751,218751,4218751,74218751,574218751,3574218751,
! %T A181539
63574218751,163574218751,163574218751,80163574218751,480163574218751,
! %U A181539
7480163574218751,87480163574218751,487480163574218751,5487480163574218751
! %N A181539 a(n) = m, an n digit number (leading zero suspended when
appropriate) such that m^2 == 1 mod 10^n and a(n-1) is a substring.
%e A181539 For n = 4; 8751^2 = 76580001 == 1 mod 10^4.
! %H A181539 Robert G. Wilson v, <a href="b181539.txt"> Table of n,
a(n) for n = 1..150 </a>.
! %K A181539 base,nonn,new
%O A181539 1,2
+ %Y A181539 Cf. A007185, A016090, A181628.
%A A181539 Kevin Batista (kevin762401(AT)yahoo.com), Oct 29 2010
%E A181539 Edited by N. J. A. Sloane, Oct 29 2010
+ %E A181539 Edited and extended by Robert G. Wilson v, (rgwv(AT)rgwv.com)
Nov 02 2010

-----Original Message-----
From: N. J. A. Sloane
Sent: Wednesday, November 03, 2010 10:44 AM
To: seqfan at list.seqfan.eu
Cc: njas at research.att.com ; rgwv at rgwv.com
Subject: Re: [seqfan] Re: correcting A181539

pointing out that it did not
match the definition, and offering to edit it.
Bob, what did you come up with?
Neil

>The current A181539 does not seem to match its definition:
>for example, why a(2)=51 and not a(2)=49 (let alone a(2)=1)?

>I would rather change the definition to:

>a(n) = smallest number m > 1 such that m^2 == 1 (mod 10^n)

>that would give a sequence:

>9, 49, 249, 1249, 18751, 218751, 781249, 24218751, 74218751,
>1425781249, 13574218751, 163574218751, 163574218751, 19836425781249,
>19836425781249, 2480163574218751, 12519836425781249,
>12519836425781249, 487480163574218751, 15487480163574218751,
>215487480163574218751, 215487480163574218751, 4784512519836425781249,
>45215487480163574218751, 45215487480163574218751

>Regards,
>Max

>On Wed, Nov 3, 2010 at 8:29 AM, Richard Mathar
><mathar at strw.leidenuniv.nl> wrote:
>>
>> Is there a way to keep the terms in http://oeis.org/classic/A181539
>> (current definition m: m^2 =1 (mod 10^n) by changing the definition? I'd
>> expect
>> some corresponding terms of http://oeis.org/classic/A181607 Â to appear,
>> but I
>> cannot figure out which modification in A181539 would do that
>> selection/matching.
>>

```