If a*1960=b**2, a and b are natural numbers and b**2 is divisible by 9, find the minimum value of a?
若a*1960=b**2，a、b为自然数且b**2能被9整除，求a的最小值？
<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

<gadget id="calculator">9 * 10</gadget>
<output>90</output>

<result>90</result>