Command line to find prime factors up to about 20-digit
echo 839371220220156165472918185637163723645455086497487793529808963523921781269796411271577345387115305325306580639336340439698459161638180539105481772724324941916666829826781812839 | ecm -n -c 74 11e3
Command line to find prime factors up to about 25-digit
echo 839371220220156165472918185637163723645455086497487793529808963523921781269796411271577345387115305325306580639336340439698459161638180539105481772724324941916666829826781812839 | ecm -n -c 214 5e4
Command line to find prime factors up to about 30-digit
echo 839371220220156165472918185637163723645455086497487793529808963523921781269796411271577345387115305325306580639336340439698459161638180539105481772724324941916666829826781812839 | ecm -n -c 430 25e4
Command line to find prime factors up to about 35-digit
echo 839371220220156165472918185637163723645455086497487793529808963523921781269796411271577345387115305325306580639336340439698459161638180539105481772724324941916666829826781812839 | ecm -n -c 904 1e6
Command line to find prime factors up to about 40-digit
echo 839371220220156165472918185637163723645455086497487793529808963523921781269796411271577345387115305325306580639336340439698459161638180539105481772724324941916666829826781812839 | ecm -n -c 2350 3e6