Can the following summation be reduced to any single formula? I tried using a few combinatorial laws such as Pascal's but nothing seems to work.
$$2\sum_{r=0}^{n-k}\binom{n-r}k\binom{k-1}r.$$
2026-05-15 05:05:58.1778821558
Counting and Combinatorics
45 Views Asked by Bumbble Comm https://math.techqa.club/user/bumbble-comm/detail AtRelated Questions in COMBINATORICS
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