This is very simple question

Al Schapira a.d.schapira at worldnet.att.net
Mon Jun 7 03:02:17 CEST 2004


Eric wrote:
> I would want to obtain a list of factors (multiples of 2) given a
> prime number in python.
> 
> For example 13=[8,4,1], 5=[4,1], 7=[4,2,1], 15=[8,4,2,1]
> 
> I would appreciate a fuction which would do this.
> 
> Eric

What you seem to want are the powers of 2 that add up to the given 
number. These are the powers of two that correspond to 1's in the binary 
representation of the given number (integer).

$ cat foo.py
powerlist = [1 << (30-i) for i in range(31)]  # [... 32, 16, 8, 4, 2, 1]

for x in [13,5,7,15,17,33]:
     print x, [x & i for i in powerlist if x & i]

$ python < foo.py
13 [8, 4, 1]
5 [4, 1]
7 [4, 2, 1]
15 [8, 4, 2, 1]
17 [16, 1]
33 [32, 1]

Is this horse dead yet?

	-Al Schapira, a.d.schapira at worldnet.att.net




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