数列1，1，2，3，5，…（从第三项开始每一项是前两项之和

public class Test { public static void main(String[] args) { int n = 5; //项目数 long n1 = 1, n2 = 1; for (int i = 3; i <= n; i++) { n2 = n1 + n2; n1 = n2 - n1; } System.out.println(n2); } }