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March 18th, 2009, 01:51 AM  #1 
Newbie Joined: Mar 2009 Posts: 13 Thanks: 0  Combinatorial Question Help?
a "codeword" from the alphabet A={0,1,2,3) is said to be legitimate if it contains even number of zeros. Thus for instance the codeword 31020 is legitimated and 0002 is not. How many n  letter codewords are legitimated ?

March 18th, 2009, 09:03 AM  #2 
Global Moderator Joined: Nov 2006 From: UTC 5 Posts: 16,046 Thanks: 938 Math Focus: Number theory, computational mathematics, combinatorics, FOM, symbolic logic, TCS, algorithms  Re: Combinatorial Question Help?
Set up a double summation that goes through each length up to n and each even number from 0 to the current length, summing the number of ways to choose the appropriate combination. You can use algebra to simplify this, if desired.


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