I have been trying to figure out a formula for the sum of combinations. For example:(adsbygoogle = window.adsbygoogle || []).push({});

[itex]\sum[/itex]^{n}_{k=0}([itex]\frac{n}{k}[/itex]) = 2^{n}

But what if you want to sum from any arbitrary k, like 4? I've tried looking at Pascal's triangle for nice values of n and k, but haven't been able to see a pattern. I would really appreciate any help with this. I want to apply this to combinations for large n, which are impractical to compute.

Thank you in advance.

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# Sum of combinations from k to n

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