Timeline for Combinatorial proof of summation of $\sum\limits_{k = 0}^n {n \choose k}^2= {2n \choose n}$
Current License: CC BY-SA 3.0
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| Feb 19, 2022 at 19:27 | comment | added | Zaz | Oh wow! Very intuitive once I finally got it. For anyone else struggling to understand this: imagine 1,1,4 and 4,1,1 grayed out so that you're left with a diamond: The number of ways of going down to the 2nd row and back up to 1 are the same as the number of ways of going down to 6. | |
| Dec 16, 2015 at 12:50 | history | answered | Amritanshu Prasad | CC BY-SA 3.0 |