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 PDP11. 

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. 

7th Edition