factor, primes - factor a number, generate large primes
SYNOPSISfactor [ number ]
primes start [ finish ]
Factor prints number and its prime factors, each repeated the proper
number of times. The number must be positive and less than 2**54
If no number is given, factor reads a stream of numbers from the stan‐
dard input and factors them. It exits on any input not a positive
integer. Maximum running time is proportional to sqrt(n).
Primes prints the prime numbers ranging from start to finish, where
start and finish are positive numbers less than 2**56. If finish is
missing, primes prints without end; if start is missing, it reads the
starting number from the standard input.