[seqfan] Re: Is this a known problem?

[israel at math.ubc.ca]

On Aug 23 2018, Tomasz Ordowski wrote:

>Dear SeqFans!
>
>The Problem:
>
>Are there odd numbers k such that k + 2^n is composite for all n ?

Dual Sierpinski numbers. Conjectured to be the same as the Sierpinski 
numbers. 
<https://en.wikipedia.org/wiki/Sierpinski_number#Dual_Sierpinski_problem>

>Let's define:
>
>Odd numbers k such that k + 2^n is composite for all n < k.

A033919.

Cheers,
Robert

>For example: k = 773, but 773 + 2^955 is prime.
>
>Cf. https://oeis.org/A139803
>
>Best regards,
>
>Thomas
>___________
>Similar to the Sierpinski numbers:
>
>https://en.wikipedia.org/wiki/Sierpinski_number
>