数学好难啊。

The sequence f(n)=(2n)! / n! is defined for all positive integer values of n. If x is defined as the product of first 10 ten terms of the sequence, which of the following is the greatest factor of x?

a.2^20

b.2^30

c. 2^45

d.2^52

e.2^55

ans. E

这道题估计不大可能在gmat出现

考试的时候没有计算器瓦

the product of first 10 ten terms of the sequence=（2！/1！）*（4!/2!)

*...(20!/10!)=(2)*(3*4)*...(11*12*13*...20)=(2^1)*(2^2*3)*（2^3*.....)*...(2^10*...)=2^55*...

P.S.:the ...means the prime integre greater than 2

So E

楼上的是正解

有没有简单的办法, 考试没有这么多的时间啊! 谢谢数学大牛.