奇数:
1,3,5,7,9,11,13,15,17,19
偶数:
2,4,6,8,10,12,14,16,18,20
质数:
2,3,5,7,11,13,17,19
合数:
4,6,8,9,10,12,14,15,16,18,20
既是奇数又是合数的:
9,15