Question

是阶乘的意思我知道,比如（2N-1）!怎么计算哈?

Answer 1

!就是阶乘的阶乘,也就是对阶乘再取阶乘.

（2n-1）!= (2n-1)(2n-2)(2n-3)...1

(2n-1)!= ((2n-1)!)!= [(2n-1)(2n-2)(2n-3)...1][(2n-1)(2n-2)(2n-3)...1-1][(2n-1)(2n-2)(2n-3)...1-2][(2n-1)(2n-2)(2n-3)...3]...1

即

3!= 3×2×1= 6

3!= （3×2×1）!=6×5×4×3×2×1=720