There are 4 different numbers that can form 18 different 4-digit numbers. Arrange these 18 different 4-digit numbers in a row from small to large, the first of which is a perfect square number, and the penultimate second is also a perfect square number. Then the average of these 18 numbers is: how much.
有4个不同的数字共可组成18个不同的4位数．将这18个不同的4位数由小到大排成一排，其中第一个是一个完全平方数，倒数第二个也是完全平方数．那么这18个数的平均数是：多少．
<gadget id="calculator">6_000 + 444</gadget>
<output>6_444</output>

<result>6_444</result>