# 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.

### Updated 28 May 2019.

This program used a library that I last updated 20 years ago. I wrote it
in assembly language for 32 bit Intel CPUs and the syntax is different
now. Binary compatibility kept it working without software maintenance
for a long time, but it no longer works.

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.