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How would I solve this problem? Thanks in advance.

Please just give the number for the answer instead of strategies, those are really unhelpful. If this is a duplicate please put a link for the answered question.

I just want a number for the answer, so far this website has been really unhelpful.


marked as duplicate by Math1000, lulu, Ross Millikan combinatorics May 26 at 0:35

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  • $\begingroup$ @Math1000 I don't really understand that solution, and I just want a number and solution for this specific case of n=10. $\endgroup$ – HelloPeople99 May 26 at 0:30
  • $\begingroup$ There are few enough you can just list and count them. It will take a little while, but you might see the pattern. If you put in $1$ you can't put in $2$ and so on. $\endgroup$ – Ross Millikan May 26 at 0:37

Such a subset of $\{1,2,\ldots,n\}$ either does not contain $n$ and hence is such a subset of $\{1,2,\ldots,n-1\}$, or it contains $10$ and the rest is such a subset of $\{1,2,\ldots, n-2\}$. Use his to find a recursion formula and recognize this. as famous


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