def is_special(n):
"""
Returns True if the number is prime.
This is only one possible implementation of "isSpecial",
used as an example. It's not an especially fast prime
checker either, but it works.
"""
if n < 2:
return False
for i in range(2, n // 2 + 1):
if n % i == 0:
# found a factor: not prime
return False
# no factors: prime
return True