arvaus = float(input("Guess a prime number: "))
while (number < arvaus) & (number >=2):
    if arvaus / number == int() :
        print(arvaus, "is a prime number.")
    else:
        print(arvaus, "is not a prime number.")

Traceback (most recent call last):
  File "C:/Python31/prime_numbers", line 2, in <module>
    while (number < arvaus) & (number >=2):
NameError: name 'number' is not defined