Use 9 numbers of 1, 2, 3, 4, 5, 6, 7, 8, 9 to form 5 numbers, each number can only be used once, so that these 5 numbers satisfy: the second number is the first 3 times the number, the third number is 5 times the first number, the fourth number is 7 times the first number, and the fifth number is 9 times the first number. So what is the first number?
用1、2、3、4、5、6、7、8、9这9个数字组成5个数，每个数字只能用一次，使这5个数满足：第二个数是第一个数的3倍，第三个数是第一个数5倍，第四个数是第一个数的7倍，第五个数是第一个数的9倍．那么第一个数是多少．
<result>9</result>