NAME

factor, primes − factor a number, generate large primes

SYNOPSIS

factor [ number ]

primes

DESCRIPTION

When factor is invoked without an argument, it waits for a number to be typed in.  If you type in a positive number less than 256 (about 7.2×1016) it will factor the number and print its prime factors; each one is printed the proper number of times. Then it waits for another number. It exits if it encounters a zero or any non-numeric character.

If factor is invoked with an argument, it factors the number as above and then exits. 

Maximum time to factor is proportional to √n
‾ and occurs when n is prime or the square of a prime.  It takes 1 minute to factor a prime near 1014 on a PDP-11. 

When primes is invoked, it waits for a number to be typed in.  If you type in a positive number less than 256 it will print all primes greater than or equal to this number. 

DIAGNOSTICS

“Ouch” for input out of range or for garbage input. 

May 16, 1980