If the number of divisors of a natural number is an odd number, we call this natural number a "hope number". Then, what is the largest "hope number" within 1000.
如果一个自然数的约数的个数是奇数，我们称这个自然数为"希望数"，那么，1000以内最大的"希望数"是多少．
<gadget id="calculator">31 ** 2</gadget>
<output>961</output>

<result>961</result>