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#### hxthanh

##### New member

- Sep 20, 2013

- 16

Define $S_3(r)$ is number of all $3\times 3$ magic square with row sum is $r$

Prove that:

$\displaystyle S_3(r)={r+2\choose 4}+{r+3\choose 4}+{r+4\choose 4}$

p/s: (sorry, if my thread wrong place)