A series of numbers: 1, 3, 6, 10, 15, 21, 28, ... Then what is the difference between the 100th and 98th numbers in this series of numbers.
一串数：1，3，6，10，15，21，28，…那么这串数的第100个与第98个数的差是多少．
<gadget id="calculator">99 + 100</gadget>
<output>199</output>

<result>199</result>