There is a series of numbers: 7, 77, 777, 7777..., add the first 77 numbers of them, then what is the last three digits of their sum.
有一列数：7、77、777、7777…，把它们的前77个数相加，那么它们和的末三位数是多少．
<gadget id="calculator">777 * 75</gadget>
<output>58_275</output>

<gadget id="calculator">58_275 + 77 + 7</gadget>
<output>58_359</output>

<result>58_359</result>