1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30

只輸出偶數數字：
2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,