The natural numbers 1, 2, 3, ... keep writing down to form a number 123456789101112... When a certain number is written, the formed number is exactly divisible by 72 for the first time. What is this number?
自然数1，2，3，…一直写下去，组成一个数123456789101112…，写到某个数的时候，所组成的数刚好第一次被72整除，这个数是多少．
<result>36</result>