Suppose that you want to find all two and three digit primes where allof the component digits are also prime (eg, 37 would qualify but 41would not, since 4 is not prime).

Here is the simple Unix approach:

factor $(seq 10 999) | awk 'NF == 2 {print $2}' | egrep '^[12357]*$'

(I won't claim that this is obvious until you're immersed