Sequence: (1/1), (2/1), (1/2), (3/1), (2/2), (1/3), (4/1), (3/2), (2/3), (1/4), ---, what is the number item of the fraction (1991/1949) in this sequence.
数列：(1/1)，(2/1)，(1/2)，(3/1)，(2/2)，(1/3)，(4/1)，(3/2)，(2/3)，(1/4)，---中，分数(1991/1949)在这个数列中位于第多少项．
<gadget id="calculator">1 / 1</gadget>
<output>1</output>

<gadget id="calculator">2 / 1</gadget>
<output>2</output>

<gadget id="calculator">2 / 2</gadget>
<output>1</output>

<gadget id="calculator">1 + 3_938</gadget>
<output>3_939</output>

<gadget id="calculator">3_938 / 2</gadget>
<output>1_969</output>

<gadget id="calculator">3_939 * 1_969</gadget>
<output>7_755_891</output>

<gadget id="calculator">7_755_891 + 1_949</gadget>
<output>7_757_840</output>

<result>7_757_840</result>