Binary Prime Numbers

I was wondering what prime numbers would look like in binary format. So, I wrote this little Python script prime.py:

import math

def int2bin(n):
    s = ''
    for i in range(0,1 + int(math.log(n, 2))):
        if n & (1 << i) > 0: s = '# ' + s
        else: s = '. ' + s
    return s

def is_prime(n):
    if n < 2: return False
    if n == 2: return True
    if n % 2 == 0: return False
    for i in range(3, int(n ** 0.5) + 1, 2):
        if n % i == 0: return False
    return True

print int2bin(2).center(32)
for i in range(3, 256, 2):
    if is_prime(i): print int2bin(i).center(32)

The output is a nicely formatted ASCII interpretation prime.txt:

      # .
      # #

     # . #
     # # #

    # . # #
    # # . #

   # . . . #
   # . . # #
   # . # # #
   # # # . #
   # # # # #

  # . . # . #
  # . # . . #
  # . # . # #
  # . # # # #
  # # . # . #
  # # # . # #
  # # # # . #

 # . . . . # #
 # . . . # # #
 # . . # . . #
 # . . # # # #
 # . # . . # #
 # . # # . . #
 # # . . . . #
 # # . . # . #
 # # . . # # #
 # # . # . # #
 # # . # # . #
 # # # . . . #
 # # # # # # #

# . . . . . # #
# . . . # . . #
# . . . # . # #
# . . # . # . #
# . . # . # # #
# . . # # # . #
# . # . . . # #
# . # . . # # #
# . # . # # . #
# . # # . . # #
# . # # . # . #
# . # # # # # #
# # . . . . . #
# # . . . # . #
# # . . . # # #
# # . # . . # #
# # . # # # # #
# # # . . . # #
# # # . . # . #
# # # . # . . #
# # # . # # # #
# # # # . . . #
# # # # # . # #

I just did a screen shot of the output, loaded it in Photoshop, and ran a "Chalk & Charcoal" Filter.