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  • \$\begingroup\$ That's interesting. As far as I can tell, the two large factors I used were primes, at least according to sympy. Do you have an example of the found factors? Did you check their product? Well done, by the way. That was the intended solution. I blame the documentation. \$\endgroup\$ Commented Oct 25, 2020 at 6:39
  • \$\begingroup\$ @EricDuminil Indeed, it seems like I did something wrong (the most likely explanation is that I accidentally removed a digit from the middle when copying the base36-decoded result from Mathematica and removing the line break it inserted) \$\endgroup\$ Commented Oct 25, 2020 at 7:03
  • \$\begingroup\$ @EricDuminil A better program could still factor the number (in around 865 seconds). \$\endgroup\$ Commented Oct 25, 2020 at 7:24
  • \$\begingroup\$ Wow. Colored me impressed. I had no idea how to estimate the time it would take to factor the semiprime, and I didn't want the target to look suspiciously long. Do you know how the required time scales? How many more bits would be required for the factorization to be 3000 times longer (~1 month)? Even then, I guess that throwing more CPUs at the problem could bring the required time to a few days. It wasn't a bruteforce question anyway. Again : congrats. \$\endgroup\$ Commented Oct 25, 2020 at 8:44
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    \$\begingroup\$ @EricDuminil I used the Wikipedia page en.wikipedia.org/wiki/RSA_numbers to check if it's feasible to factorize the number (and it said that a 100-digit prime can be factored in 72 minutes on an old CPU). It seems that a 250-digit number is the largest one factored, and it was factored in February 2020. It also seems that it took them around 2700 core-years and they used cado-nfs. \$\endgroup\$ Commented Oct 25, 2020 at 9:01