There is a column of numbers, the first number is 6, and each subsequent number is 3 greater than the previous number. Please do the math, how many numbers in this column are 81.
有一列数，第一个是6，后面每一个数都比前面一个数大3，请你算一算，这列数中，第多少个数是81．
<gadget id="calculator">81 - 6</gadget>
<output>75</output>

<gadget id="calculator">75 / 3</gadget>
<output>25</output>

<gadget id="calculator">25 + 1</gadget>
<output>26</output>

<result>26</result>