Andy:

> I reckon the best few exponents of around

> the same size are: 65520, 75600, 69300,

> 83160, 73920, 70560 then 64680.

Then recall that Paul U restricted his

search of 2^a-2^b-1 to b<=40.

So that gives 280 chances for those 7

values of c=a-b, whereas

ln(N) ~ ln(2^70000) = 50,000,

giving you odds of order 100:1 against.

It's neat that one of your 280 showed up,

with b=15, and even neater that Bouk's eagle

eyes spotted it in Henri's pages.

PS: How's the latest GRU cooking?

Remember that Phil has just offered

double the usual extra bits,

if/when you need them :-)

Also Paul L was holding NFS cycles

in reserve for 2^15*(2^64680-1)-1

which we didn't need. So maybe

you could do something really

impressive with another 150 digits

from him, in some strategic place :-?

Best wishes

David