ENH: Enhanced the problem set building on the image handing and arrays. Illustrated dtypes, casting and their importance along with an example using RGBA images. Also introduce edge detection.

a = int( raw_input( 'Enter number: ') )
while a != 4:
    print a,
    if a % 2 == 1:
        a = a * 3 + 1
    else:
        a /= 2
print 4, 2, 1