I have a nested sum like so:
k∗∑k1=k0 ...k∗∑kn=kn−1⏟n times1 with n,k0,k∗∈N, k∗≥k0
Is there a general, shorter representation that spares me calculating the actual sums?
Answer
\displaystyle\sum_{k_0\le k_1\le\cdots\le k_n\le k^*}1=\sum_{1\le k_1-k_0+1< k_2-k_0+2<\cdots< k_n-k_0+n\le k^*-k_0+n}1={k^*-k_0+n\choose n}
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