修改之後的：

public static void main(String[] args) { // TODO Auto-generated method stub

int i=1;

BigDecimal big = new BigDecimal(0);

double m;

while(i<=20){

m=fun(i);

double temp = 1/m;

big = big.add(BigDecimal.valueOf(temp));

i++;

}

System.out.println(big);

}

private static double fun(long i) {

// TODO Auto-generated method stub

int n=1;

double s=1;

while(n<=i){

s=s*n;

n++;

}

return s;

}

輸出結果：1.7182818284590452257701727507883965

這樣更精確點 當然你可以把BigDecimal換成double也行，只不過精確度不夠