The first test of this year's "Hope Cup" National Mathematics Invitational Competition was held on March 15th. Observe the following series of numbers: (1/1), (1/2), (2/1), (1/3), ( 2/2), (3/1), (1/4), (2/3), (3/2), (4/1), (1/5), (2/4), (3/ 3), (4/2), (5/1)...According to the found rule, counting from left to right, what number is (3/15)?
本届"希望杯"全国数学邀请赛第1试于3月15日举行，观察下面的一列数：(1/1)，(1/2)，(2/1)，(1/3)，(2/2)，(3/1)，(1/4)，(2/3)，(3/2)，(4/1)，(1/5)，(2/4)，(3/3)，(4/2)，(5/1)…根据发现的规律，从左向右数，(3/15)是第多少个数．
<gadget id="calculator">16 + 1</gadget>
<output>17</output>

<gadget id="calculator">16 / 2</gadget>
<output>8</output>

<gadget id="calculator">17 * 8</gadget>
<output>136</output>

<gadget id="calculator">136 + 3</gadget>
<output>139</output>

<result>139</result>