Command line to find prime factors up to about 20-digit
echo 509971167541375334985748604826163473559683444227399662380061076968731609027129650727327557970801041422490240747518154149681971022014840734145281344185145848341 | ecm -n -c 74 11e3
Command line to find prime factors up to about 25-digit
echo 509971167541375334985748604826163473559683444227399662380061076968731609027129650727327557970801041422490240747518154149681971022014840734145281344185145848341 | ecm -n -c 214 5e4
Command line to find prime factors up to about 30-digit
echo 509971167541375334985748604826163473559683444227399662380061076968731609027129650727327557970801041422490240747518154149681971022014840734145281344185145848341 | ecm -n -c 430 25e4
Command line to find prime factors up to about 35-digit
echo 509971167541375334985748604826163473559683444227399662380061076968731609027129650727327557970801041422490240747518154149681971022014840734145281344185145848341 | ecm -n -c 904 1e6
Command line to find prime factors up to about 40-digit
echo 509971167541375334985748604826163473559683444227399662380061076968731609027129650727327557970801041422490240747518154149681971022014840734145281344185145848341 | ecm -n -c 2350 3e6