Command line to find prime factors up to about 40-digit
echo 686375447369711232043928028631661518850811393832426337206451929205275285581212923469137618277197627102024807569740648134529587684463401480609893611805657694759033191155562092464578124233955973917733 | ecm -n -c 2018 3e6
Command line to find prime factors up to about 45-digit
echo 686375447369711232043928028631661518850811393832426337206451929205275285581212923469137618277197627102024807569740648134529587684463401480609893611805657694759033191155562092464578124233955973917733 | ecm -n -c 4409 11e6
Command line to find prime factors up to about 50-digit
echo 686375447369711232043928028631661518850811393832426337206451929205275285581212923469137618277197627102024807569740648134529587684463401480609893611805657694759033191155562092464578124233955973917733 | ecm -n -c 7541 43e6
Command line to find prime factors up to about 55-digit
echo 686375447369711232043928028631661518850811393832426337206451929205275285581212923469137618277197627102024807569740648134529587684463401480609893611805657694759033191155562092464578124233955973917733 | ecm -n -c 17767 11e7