Command line to find prime factors up to about 20-digit
echo 15159978398253593344825911164591246862926799264607272003481374277905250397310855546664187525785667901178698609930590639490945265521886299849320035876678068475100468972565852953 | ecm -n -c 74 11e3
Command line to find prime factors up to about 25-digit
echo 15159978398253593344825911164591246862926799264607272003481374277905250397310855546664187525785667901178698609930590639490945265521886299849320035876678068475100468972565852953 | ecm -n -c 214 5e4
Command line to find prime factors up to about 30-digit
echo 15159978398253593344825911164591246862926799264607272003481374277905250397310855546664187525785667901178698609930590639490945265521886299849320035876678068475100468972565852953 | ecm -n -c 430 25e4
Command line to find prime factors up to about 35-digit
echo 15159978398253593344825911164591246862926799264607272003481374277905250397310855546664187525785667901178698609930590639490945265521886299849320035876678068475100468972565852953 | ecm -n -c 904 1e6
Command line to find prime factors up to about 40-digit
echo 15159978398253593344825911164591246862926799264607272003481374277905250397310855546664187525785667901178698609930590639490945265521886299849320035876678068475100468972565852953 | ecm -n -c 2350 3e6