Among the 20 natural numbers 1, 2, 3, 4, ..., 20, the sum of any ten numbers is multiplied by the sum of the other ten numbers, how many different products can be obtained.
在1、2、3、4、…、20这20个自然数中，任取十个数相加的和与其余十个数相加的和相乘，能得到不同的乘积多少个．
<gadget id="calculator">155 - 55</gadget>
<output>100</output>

<gadget id="calculator">100 / 2</gadget>
<output>50</output>

<gadget id="calculator">50 + 1</gadget>
<output>51</output>

<result>51</result>