n => 2n+1 to get prime: seed = 73

[Don Reble]

> Dear Seqfans,
> The operation n => 2n+1 quickly gives primes for most "seed" values of n.
> But for some seeds, the transformed numbers keep being composite.
> The first "tough" number is n=73.
> Can the n =>2n+1 transformation, in this particular case,
>  lead to prime number (and when?),

Starting from 73, the 2552nd number (74 * 2^2552 - 1) is prime. It's a
771-digit number which begins and ends 12525...16703.

See also A040081.

-- 
Don Reble  djr at nk.ca