Smallest known CPAP-7 at 33 digits
- Harvey Dubner has found the smallest known CPAP-7 with a program by me:
149143516628800164802930723713131 + 210n, n=0..6
The old record from 1997 was 37 digits by Dubner alone.
The difference in a CPAP-7 must be at least 210, meaning 209*6=1254 composites
are required. This makes small CPAP-7 much harder than larger ones, and the
minimal CPAP-7 currently seems out of reach.
The expectation was 23 GHz days to find around 1 million AP-7 before a CPAP-7.
The GMP library was used for prp testing and Marcel Martin's Primo proved the
primes. Also thanks to Paul Zimmermann for discussions about the problem.
The smallest known CPAP-k are listed here:
Torbjörn Alm has earlier found the smallest known CPAP-8 with my program,
without an announcement.
Any CPAP-9 or -10 is hard and I have not heard of any searches for small cases.
Jens Kruse Andersen