Prime Factors of Integers


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This is just a toy to factor some integers. The source code is available for your amusement. This runs on a very slow machine and may take a long time to return your answers. Prime numbers will take the longest. If a number has small prime factors, it will take less time than if it has at least two large prime factors. For example, 123456789012345678901234567890 has 2906161 as its largest prime factor and 3803 as its second largest prime factor and takes about 5 seconds to factor if the machine is not busy. 1234567890123456789012345678901234567890 takes almost 3 minutes of CPU time. If the integer you supply is prime and more than 14 digits, it may take so long to factor that your connection times out.

The integer

Send email to John Moyer, jrm@rsok.com.
John Moyer's home page
At RSA, an explanation of what factoring means.
Print all of the primes within a range of integers. These are from a file containing all of the primes less than 2000000000.

Source code for a sieve program:
sieve2310.c or embedded in html for easy viewing with Internet Explorer sieve2310.c.html or to ftp sieve2310.c or to ftp a 32bit ".EXE" file and source for Microsoft Windows sieve2310.exe


Copyright © 1996, John Moyer, All rights reserved.