{"trustable":true,"prependHtml":"\u003cscript\u003e\n window.katexOptions \u003d {\n delimiters: [\n {left: \u0027\\\\(\u0027, right: \u0027\\\\)\u0027, display: false},\n ]\n };\n\u003c/script\u003e\n","sections":[{"title":"","value":{"format":"HTML","content":"\u003cp\u003eBaoBao and his $(n-1)$ classmates are going to the park. For convenience, their teacher DreamGrid has numbered the students from 1 to $n$ and decides to form the students into some groups, where each group consists of exactly two students.\u003c/p\u003e\n\u003cp\u003eFor some reason, DreamGrid requires that the indices of the two students in the same group should have a common divisor greater than 1. Note that each student can only belong to at most one group, and it\u0027s not necessary that every student belongs to a group.\u003c/p\u003e\n\u003cp\u003ePlease help DreamGrid form as many groups as possible.\u003c/p\u003e\n\n\u003ch4\u003eInput\u003c/h4\u003e\n\u003cp\u003eThere are multiple test cases. The first line of the input contains an integer $T$, indicating the number of test cases. For each test case:\u003c/p\u003e\n\u003cp\u003eThe first and only line contains an integer $n$ ($1 \\le n \\le 10^5$), indicating the number of students.\u003c/p\u003e\n\u003cp\u003eIt\u0027s guaranteed that the sum of $n$ of all test cases will not exceed $10^6$.\u003c/p\u003e\n\n\u003ch4\u003eOutput\u003c/h4\u003e\n\u003cp\u003eFor each test case output one line. The line first contains an integer $k$ indicating the number of groups, then $2k$ integers $a_1, a_2, \\dots, a_{2k}$ follow, indicating that student $a_1$ and $a_2$ belong to the same group, student $a_3$ and $a_4$ belong to the same group, ..., student $a_{2k-1}$ and $a_{2k}$ belong to the same group. The integers in a line are separated by a space. If there are multiple valid answers, you can print any of them.\u003c/p\u003e\n\u003cp\u003ePlease, DO NOT output extra spaces at the end of each line, or your solution may be considered incorrect!\u003c/p\u003e\n\n\u003ch4\u003eSample\u003c/h4\u003e\n\u003ctable class\u003d\"vjudge_sample\"\u003e\n\u003cthead\u003e\n \u003ctr\u003e\n \u003cth\u003eInput\u003c/th\u003e\n \u003cth\u003eOutput\u003c/th\u003e\n \u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\u003cpre\u003e3\n1\n4\n6\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003e0\n1 2 4\n2 2 4 3 6\n\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\n"}}]}