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Homework Help: Proofs involving Catalan Numbers

  1. Apr 7, 2008 #1
    1. The problem statement, all variables and given/known data

    I need to prove two things about the Catalan numbers. The first is that Cn is odd iff n=(2^k)-1 for some positive integer k.

    The second is that given the matrix A defined by the rule a(i,j)=C(i+j), prove that det A=1. I have not covered determinants in my linear class yet, so I do not have any idea what to do with this one.

    2. Relevant equations



    3. The attempt at a solution

    I am assuming that both proceed by induction. The first one seems to be more direct, but I am really lost as to how to proceed with both. Any help or suggestions is greatly appreciated. Thanks a lot!
     
  2. jcsd
  3. Apr 7, 2008 #2

    HallsofIvy

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    I would start by writing down the definition of Catalan numbers!
     
  4. Apr 7, 2008 #3
    Sorry. The Catalan numbers are 1,1,2,5,14,42,... given by the formula Cn=(1/(n+1))*2n choose n. With 2n choose n equal to (2n)!/(n!n!). Sorry for the bad form, I don't have any math writing program.
     
  5. Apr 7, 2008 #4

    HallsofIvy

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    That's
    [tex]\frac{1}{n+1}\frac{(2n)!}{n!n!}[/tex]
    Click on that to see the code. You don't need a "math writing program" on your own computer.
     
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