Calculation: 1*3+2*4+3*5+4*6+5*7+...+17*19+18*20=how much.
计算：1*3+2*4+3*5+4*6+5*7+…+17*19+18*20=多少．
<gadget id="calculator">20 / 3</gadget>
<output>20/3 = around 6.666667</output>

<gadget id="calculator">18 * 19 * (20/3)</gadget>
<output>2_280</output>

<gadget id="calculator">171 + 2_280</gadget>
<output>2_451</output>

<result>2_451</result>