[QUOTE=c10ck3r;368096]That depends. Do you have an idea of when it will yield a prime? :P[/QUOTE]

As TheCount said, not likely before n=1M. But you never know. You might get lucky. So let me rephrase: If you don't find a prime, do you have an idea of how high you plan to test it? If so, I might be able to give you a closer idea to an optimum sieve limit.

Edit: It appears that for the range of n=200K-1M, you should find, on average, .0895 of a prime, which gives you ~8.56% chance of finding a prime in the range. This includes the n=200K-250K range that you have already searched so it is now less than that. It's tough going for very low-weight bases.

[QUOTE=TheCount;368112]I would expect 1 prime for 8*263^n+1 on average between n=250,000 and 455,000,000,000,000.
S263 is the 6th lowest weight base, and so while fast to test for a range its chance of prime is pretty low. Plenty of other fish in the sea.[/QUOTE]

This is a little worse than what I got but in relative terms, it gives a pretty good idea of the difficulty. In doing a fairly quick sieve to P=625G for n=200K-1M, which left 5138 terms, I found that one prime should be found for n=200K to ~13T. Since my estimate assumes that n=200K-250K wasn't already tested, it comes out a little better than your estimate for n=250K to 455T. To arrive at my estimate, I found that .0895 of a prime should be found for n=200K-1M and .128 of a prime should be found for each power of 10 in the n-range after that, i.e. .128 of a prime for n=1M-10M, 10M-100M, etc. (You might see what you came up with for each power of 10 in the n-range because even small differences in such an estimate make a big difference in the overall estimate.) Taking it further, even though ~1 prime is expected for n=200K-13T, there is only a 63% chance of actually finding one for the range.

This kind of gives people an idea of the difficulty in proving many of these bases. Albeit it is a very low-weight k for S263, it is only one k remaining. Imagine the difficulty of proving many bases with 5-10 k's remaining at n=100K or 200K, even if several of the k's are much higher weight.

Extending my R262 reservation from n=25k to n=50k

Reserving R333.

R366 tested n=600k-700k, no prime. Continuing...

S263 tested to 300k. Continuing.

Mark has completed S376, S380, and S470 to n=100K. 3 primes were found for n=50K-100K shown [URL="http://www.mersenneforum.org/showpost.php?p=371235&postcount=1213"]here[/URL]. The bases are released.

Mathew has completed S430 to n=150K; 2 primes were found for n=100K-150K shown below; 3 k's remain.

Primes:
19125*430^116506+1
5370*430^134491+1

The excellent run continues with only 3 k's remaining for a base with CK=22413 !

He is extending the reservation for S430 to n=200K and is also reserving R430 to n=100K.

reservation
 

I would like to start S335 and S461 to 50K.

[QUOTE=MagentaSunrise;371320]I would like to start S335 and S461 to 50K.[/QUOTE]

Both bases on the Riesel and Sierp sides have already been searched to n>50K or proven. Can you check? Thanks.

[QUOTE=gd_barnes;371338]Both bases on the Riesel and Sierp sides have already been searched to n>50K or proven. Can you check? Thanks.[/QUOTE]

Wow! sorry about that.
I meant S355 and S431