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HDOJ 1098 Ignatius's puzzle

Problem Description

Ignatius is poor at math,he falls across a puzzle problem,so he has no choice but to appeal to Eddy. this problem describes that:f(x)=5*x^13+13*x^5+k*a*x,input a nonegative integer k(k<10000),to find the minimal nonegative integer a,make the arbitrary integer x ,65|f(x)if

no exists that a,then print “no”.

Input

The input contains several test cases. Each test case consists of a nonegative integer k, More details in the Sample Input.

Output

The output contains a string “no”,if you can’t find a,or you should output a line contains the a.More details in the Sample Output.

Sample Input

11

100

9999

Sample Output

22

no

43

题目大意:方程f(x)=5*x^13+13*x^5+k*a*x;输入任意一个数k,是否存在一个数a,对任意x都能使得f(x)能被65整除。

现假设存在这个数a ,因为对于任意x方程都成立

所以,当x=1时f(x)=18+ka

又因为f(x)能被65整出,故设n为整数

可得,f(x)=n*65;

即:18+ka=n*65;

因为n为整数,若要方程成立

则问题转化为,

对于给定范围的a只需要验证,

是否存在一个a使得(18+k*a)%65==0

所以容易解得

注意,这里有童鞋不理解为什么a只需到65即可

因为,当a==66时

也就相当于已经找了一个周期了,所以再找下去也找不到适当的a了