[C++] Nested Radical Constant

做高数助教被天煞的大一学生坑了，发现是个未解问题，没有解析解。。

用C搞了下，就是这样。。。

No closed-form expression is known for this constant (Finch 2003, p. 8; S. Plouffe, pers. comm., Aug. 29, 2008).

/*****************************************
*@: Nested Radical Constant 嵌套根式常数
*@: http://mathworld.wolfram.com/NestedRadicalConstant.html
*****************************************/
#include "stdafx.h"
#include <stdio.h>
#include <math.h>
void main(void){
	int N = 10;
	int idx = 0;
	double an = 0;
	double temp = 0;

	an = sqrt(double(N));
	for(idx =(N-1);idx >= 1; idx--){
		temp = idx + an;
		an = sqrt(temp);
	}
	printf("N=%d,an=%f \n",N,an);
	getchar();
}