参考文献

https://en.wikipedia.org/wiki/Eulerian_number, 閲覧日 2022-03-13, https://en.wikipedia.org/wiki/Eulerian_number
https://math.stackexchange.com/questions/1300907/prove-sum-limits-k-1n-an-kxk-1-choose-n-xn, 閲覧日 2022-03-13, https://math.stackexchange.com/questions/1300907/prove-sum-limits-k-1n-an-kxk-1-choose-n-xn