Select a number with no factors (5)
I believe the answer is:
prime
'select' is the definition.
(I know that select can be written as prime)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for prime that I've seen before include "Main - charge" , "Foremost" , "put in the picture" , "Two or three, for example" , "Best quality, perhaps of beef" .)