73 -> 2n+1 ever prime?

[Warut Roonguthai]

On 19 Dec 1999, Christian G.Bower wrote:

> I was looking at the EIS and found sequence A051914 where Neil was
> seeking clarification. So I worked out what its meaning and that led
> to the following computation.
> 
> Take 73 then iterate f(n)=2n+1 on the value to get
> 
> 147 295 591 1183 ...
> 
> until I get a value that's prime.
> 
> So far I'm up to
> 
> 6759445072655425996692042351312808965908688011263
> 
> without finding one.
> 
> Perhaps someone with a smart prime testing algorithm can do the search
> or someone with some theoretical knowledge can tell me the search is
> in vain.
> 
> Christian

I don't understand the definition of A051914, but I probably have the
solution to your question.  After 2552 iterations, I reached a 771-digit
probable prime.  I found this with the recurrence mode of Chris Nash's
PrimeForm which is available at

http://pages.prodigy.net/chris_nash/primeform.html