推理过程 //2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 69 71 73 79 81 83 97 // 1 2 2 4 2 4 2 4 6 4 6 2 6 2 4 2 4 6 6 2 //8 9 10 11 //1!=1,2,3,4,6,12,18 //2!=1,2,3,4,5,7,9 //3!=1,2,3,4,5, //4!=1,3,4,5,6,7 //0 1 2 3 //7 6 5 4 3 2 1 //1 2 3 4 5 6 7 //1->5 2->6 3->7 //4 5 6 7 1 2 3 //5 6 7 8 1 2 3 4