[seqfan] Re: A015938 and A015939

Olivier Gerard olivier.gerard at gmail.com
Mon Aug 1 11:17:17 CEST 2011

The definitions are incorrect but I guessed A015938 from the fact that
it is close to 2^n.

a(n) is the first number greater than 2^n divisible by n:

This Mathematica program will give you A015938, starting with n=1

Table[(k = 1; While[Mod[2^n + k, n] != 0, k++]; 2^n + k), {n, 1, 10}]

For A015839, it shares a lot with the list of offsets:

Table[(k=1;While[Mod[2^n+k,n]!=0 ,k++]; k),{n,1,20}]

{1,2,1,4,3,2,5,8,1,6,9,8,11,10,7,16,15,8,17,4}

and something closer to the definition contributes correct elements
but not all the time.

Table[(k=1;While[Mod[2^n+k,n]!=0 || IntegerQ[Log[2,k]],k++]; k),{n,1,20}]

{3,6,7,12,3,14,5,24,10,6,9,20,11,10,7,48,15,26,17,24}

but not quite, and the reference to "not of the form 2^n" is curious because
A015939 contains a lot of powers of 2.

Olivier

On Mon, Aug 1, 2011 at 09:20, Max Alekseyev <maxale at gmail.com> wrote:
> Does anybody understand how A015938 and A015939 were obtained?
> The definitions do not seem to match the listed terms.
> In particular, the definition of A015938 should have produced the
> sequence of all ones.
> Regards,
> Max
>
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