(coreutils.info)factor invocation

25.1 `factor': Print prime factors
==================================

`factor' prints prime factors.  Synopses:

     factor [NUMBER]...
     factor OPTION

   If no NUMBER is specified on the command line, `factor' reads
numbers from standard input, delimited by newlines, tabs, or spaces.

   The only options are `--help' and `--version'.  Note: Common
options.

   The algorithm it uses is not very sophisticated, so for some inputs
`factor' runs for a long time.  The hardest numbers to factor are the
products of large primes.  Factoring the product of the two largest
32-bit prime numbers takes about 80 seconds of CPU time on a 1.6 GHz
Athlon.

     $ p=`echo '4294967279 * 4294967291'|bc`
     $ factor $p
     18446743979220271189: 4294967279 4294967291

   Similarly, it takes about 80 seconds for GNU factor (from
coreutils-5.1.2) to "factor" the largest 64-bit prime:
     $ factor 18446744073709551557
       18446744073709551557: 18446744073709551557

   In contrast, `factor' factors the largest 64-bit number in just over
a tenth of a second:

     $ factor `echo '2^64-1'|bc`
     18446744073709551615: 3 5 17 257 641 65537 6700417

   An exit status of zero indicates success, and a nonzero value
indicates failure.