Among the 100 natural numbers 1, 2, 3, ... 100, how many different ways are there to take two different numbers so that their sum is a multiple of 7?
在1，2，3，…100这100个自然数中，取两个不同的数，使得它们的和是7的倍数，共有多少种不同的取法．
<gadget id="calculator">15 * 14</gadget>
<output>210</output>

<gadget id="calculator">14 * 14</gadget>
<output>196</output>

<gadget id="calculator">13 / 2</gadget>
<output>13/2 = around 6.5</output>

<gadget id="calculator">14 * (13/2)</gadget>
<output>91</output>

<gadget id="calculator">210 + 210 + 196 + 91</gadget>
<output>707</output>

<result>707</result>