There are three consecutive four-digit positive integers, the middle one is a perfect square number, and the sum of the three numbers is divisible by 15, what is the minimum value of the middle number.
有三个连续的四位正整数，中间一个为完全平方数，且三个数的和能被15整除，则中间的数的最小值是多少．
<gadget id="calculator">49 * 25</gadget>
<output>1_225</output>

<result>1_225</result>