83660*72^83660-1 is the worlds largest known generalized woodall prime

that is not base 2.

at 155,390 digits it is over 30,000 digits larger than the 'old'

record that was announced only one week ago.

i proved it prime with proth 7.1, cause it is a bit faster on my

machines than the newest pfgw. for sieving i used the excellent

multisive.exe.

the search took approx two month on my 2400+ and my 1800+ athlon.

long time ago when the searchlimit was way below 60,000 i used two

dumb formulas (based on the last known primes of form n*72^n-1) to

tell me where to find the next prime of the given form. the fist said

at n=87,684 the second said n=84,924. not bad, as you can see now.

if i only believed in the formulas i would have found it earlier. but

i didn't, and pushed up the search limit instead.

also i noticed: the three largest known n making n*72^n-1 prime

(n=23560,n=48820, and now n=83660) are all n=0 (mod 10).

there remain 900+ untested candidates below 83,660. but maybe i use my

dumb formulas again to predict the next larger gen woodall and then

prp all candidates that are n=0 (mod 10) in a range around that point. :-)

thomas wolter