Find the rules and fill in the numbers: 1, 5, 9, 13, 17, 21, 25... What is the 51st number.
找规律填数：1、5、9、13、17、21、25…第51个数是多少．
<gadget id="calculator">51 - 1</gadget>
<output>50</output>

<gadget id="calculator">50 * 4</gadget>
<output>200</output>

<gadget id="calculator">1 + 200</gadget>
<output>201</output>

<result>201</result>