只有一句话的、很简单的数学题(没想出来…) - 辕门射虎


	djgan (蓝色征途)


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发表于 2007-3-12 14:47 资料个人空间短消息看全部作者

回复 #9 天宫公主的帖子

发现用MATLAB判断2^(2^5)是否质数会报错：

>> X=1:4

X =

   1    2    3    4

>> Y= 2.^(2.^X) +1

Y =

         5       17       257    65537

>> isprime(Y)

ans =

   1    1    1    1 ％可以判断X＝1，2，3，4时候，Y都是质数

>> X=1:5

X =

   1    2    3    4    5

>> Y= 2.^(2.^X) +1

Y =

  1.0e+009 *

0.0000 0.0000 0.0000 0.0001 4.2950

>> isprime(Y)
??? Error using ==> isprime
The maximum value of X allowed is 2^32.  ％2^(2^5) 就没法判断了

而且无法求2^(2^5) + 1的因子
>> factor(2^(2^5) + 1);
??? Error using ==> factor
The maximum value of n allowed is 2^32.

>>help factor
FACTOR Prime factors.
FACTOR(N) returns a vector containing the prime factors of N.

This function uses the simple sieve approach. It may require large
memory allocation if the number given is too big. Technically
it is possible to improve this algorithm, allocating less
memory for most cases and resulting in a faster execution
time. However, it will still have problems in the worst
case, so we choose to impose an upper bound on the input number
and error out for n > 2^32.

[ 本帖最后由 djgan 于 2007-3-12 14:51 编辑 ]

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