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$\sum_{l=0}^{k/2} \frac{k!}{(k-2l)!l!}$

I want to calculate the above sum. Its form is similar to that of binomial but not same.

How to calculate it? Am I in wrong path?(which means its solution is not relevant to binomial?)

kyle
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1 Answers1

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$$1=1\\ 1+1=2\\ 1+6+1=8\\ 1+10+5=16\\ 1+15+15+1=32$$

isn't this enough ?

  • Im sorry but I cant understand how that numbers are related to the solution. Could you give me little bit more? – kyle Apr 24 '17 at 08:13
  • Last hint: Pascal. –  Apr 24 '17 at 08:35
  • I totally cant understand what your intention is. I know that is pascals triangle. And I know it is related to binomial coefficient. But I cant understand how that is related to my question. I tried as best as I can to change it into the form that fits it but I cant. Thats why I questioned it here. I also cant understand how the numbers you show is related to my question. I calculate the sum of my question when k = 0 , 1 ,2 ,3, 4 ... and it doesn`t fit yours at all. – kyle Apr 24 '17 at 09:25
  • ah... hey, are you thinking that my question is $\sum_{l=0}^{k/2} \frac{k!}{(k-2l)!(2l)!}$ ? – kyle Apr 24 '17 at 09:33
  • @kyle: bingo! :) –  Apr 26 '17 at 13:50