約数を求める問題が360問ほどあります。ファイルは問題、解答の順です。ページ番号はありませんが問題と解答の順番は同じです。
約数表
| 数 | 約数 | 約数の個数 | 素数 |
|---|---|---|---|
| 1 | 1 | 1 | × |
| 2 | 1, 2 | 2 | ◯ |
| 3 | 1, 3 | 2 | ◯ |
| 4 | 1, 2, 4 | 3 | × |
| 5 | 1, 5 | 2 | ◯ |
| 6 | 1, 2, 3, 6 | 4 | × |
| 7 | 1, 7 | 2 | ◯ |
| 8 | 1, 2, 4, 8 | 4 | × |
| 9 | 1, 3, 9 | 3 | × |
| 10 | 1, 2, 5, 10 | 4 | × |
| 11 | 1, 11 | 2 | ◯ |
| 12 | 1, 2, 3, 4, 6, 12 | 6 | × |
| 13 | 1, 13 | 2 | ◯ |
| 14 | 1, 2, 7, 14 | 4 | × |
| 15 | 1, 3, 5, 15 | 4 | × |
| 16 | 1, 2, 4, 8, 16 | 5 | × |
| 17 | 1, 17 | 2 | ◯ |
| 18 | 1, 2, 3, 6, 9, 18 | 6 | × |
| 19 | 1, 19 | 2 | ◯ |
| 20 | 1, 2, 4, 5, 10, 20 | 6 | × |
| 21 | 1, 3, 7, 21 | 4 | × |
| 22 | 1, 2, 11, 22 | 4 | × |
| 23 | 1, 23 | 2 | ◯ |
| 24 | 1, 2, 3, 4, 6, 8, 12, 24 | 8 | × |
| 25 | 1, 5, 25 | 3 | × |
| 26 | 1, 2, 13, 26 | 4 | × |
| 27 | 1, 3, 9, 27 | 4 | × |
| 28 | 1, 2, 4, 7, 14, 28 | 6 | × |
| 29 | 1, 29 | 2 | ◯ |
| 30 | 1, 2, 3, 5, 6, 10, 15, 30 | 8 | × |
| 31 | 1, 31 | 2 | ◯ |
| 32 | 1, 2, 4, 8, 16, 32 | 6 | × |
| 33 | 1, 3, 11, 33 | 4 | × |
| 34 | 1, 2, 17, 34 | 4 | × |
| 35 | 1, 5, 7, 35 | 4 | × |
| 36 | 1, 2, 3, 4, 6, 9, 12, 18, 36 | 9 | × |
| 37 | 1, 37 | 2 | ◯ |
| 38 | 1, 2, 19, 38 | 4 | × |
| 39 | 1, 3, 13, 39 | 4 | × |
| 40 | 1, 2, 4, 5, 8, 10, 20, 40 | 8 | × |
| 41 | 1, 41 | 2 | ◯ |
| 42 | 1, 2, 3, 6, 7, 14, 21, 42 | 8 | × |
| 43 | 1, 43 | 2 | ◯ |
| 44 | 1, 2, 4, 11, 22, 44 | 6 | × |
| 45 | 1, 3, 5, 9, 15, 45 | 6 | × |
| 46 | 1, 2, 23, 46 | 4 | × |
| 47 | 1, 47 | 2 | ◯ |
| 48 | 1, 2, 3, 4, 6, 8, 12, 16, 24, 48 | 10 | × |
| 49 | 1, 7, 49 | 3 | × |
| 50 | 1, 2, 5, 10, 25, 50 | 6 | × |
| 51 | 1, 3, 17, 51 | 4 | × |
| 52 | 1, 2, 4, 13, 26, 52 | 6 | × |
| 53 | 1, 53 | 2 | ◯ |
| 54 | 1, 2, 3, 6, 9, 18, 27, 54 | 8 | × |
| 55 | 1, 5, 11, 55 | 4 | × |
| 56 | 1, 2, 4, 7, 8, 14, 28, 56 | 8 | × |
| 57 | 1, 3, 19, 57 | 4 | × |
| 58 | 1, 2, 29, 58 | 4 | × |
| 59 | 1, 59 | 2 | ◯ |
| 60 | 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60 | 12 | × |
| 61 | 1, 61 | 2 | ◯ |
| 62 | 1, 2, 31, 62 | 4 | × |
| 63 | 1, 3, 7, 9, 21, 63 | 6 | × |
| 64 | 1, 2, 4, 8, 16, 32, 64 | 7 | × |
| 65 | 1, 5, 13, 65 | 4 | × |
| 66 | 1, 2, 3, 6, 11, 22, 33, 66 | 8 | × |
| 67 | 1, 67 | 2 | ◯ |
| 68 | 1, 2, 4, 17, 34, 68 | 6 | × |
| 69 | 1, 3, 23, 69 | 4 | × |
| 70 | 1, 2, 5, 7, 10, 14, 35, 70 | 8 | × |
| 71 | 1, 71 | 2 | ◯ |
| 72 | 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, 72 | 12 | × |
| 73 | 1, 73 | 2 | ◯ |
| 74 | 1, 2, 37, 74 | 4 | × |
| 75 | 1, 3, 5, 15, 25, 75 | 6 | × |
| 76 | 1, 2, 4, 19, 38, 76 | 6 | × |
| 77 | 1, 7, 11, 77 | 4 | × |
| 78 | 1, 2, 3, 6, 13, 26, 39, 78 | 8 | × |
| 79 | 1, 79 | 2 | ◯ |
| 80 | 1, 2, 4, 5, 8, 10, 16, 20, 40, 80 | 10 | × |
| 81 | 1, 3, 9, 27, 81 | 5 | × |
| 82 | 1, 2, 41, 82 | 4 | × |
| 83 | 1, 83 | 2 | ◯ |
| 84 | 1, 2, 3, 4, 6, 7, 12, 14, 21, 28, 42, 84 | 12 | × |
| 85 | 1, 5, 17, 85 | 4 | × |
| 86 | 1, 2, 43, 86 | 4 | × |
| 87 | 1, 3, 29, 87 | 4 | × |
| 88 | 1, 2, 4, 8, 11, 22, 44, 88 | 8 | × |
| 89 | 1, 89 | 2 | ◯ |
| 90 | 1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45, 90 | 12 | × |
| 91 | 1, 7, 13, 91 | 4 | × |
| 92 | 1, 2, 4, 23, 46, 92 | 6 | × |
| 93 | 1, 3, 31, 93 | 4 | × |
| 94 | 1, 2, 47, 94 | 4 | × |
| 95 | 1, 5, 19, 95 | 4 | × |
| 96 | 1, 2, 3, 4, 6, 8, 12, 16, 24, 32, 48, 96 | 12 | × |
| 97 | 1, 97 | 2 | ◯ |
| 98 | 1, 2, 7, 14, 49, 98 | 6 | × |
| 99 | 1, 3, 9, 11, 33, 99 | 6 | × |
| 100 | 1, 2, 4, 5, 10, 20, 25, 50, 100 | 9 | × |
・素数とは約数が2個（1と自分自身のみ）しかない数をいう。
・平方数の約数は奇数個の約数を持つ。
・約数の個数が12個ある数（60、72、84、90、96）に注意。
約数は2つの数の積に分解して求める。例えば96は以下のように縦に分解する。
96 = 1 × 96
= 2 × 48
= 3 × 32
= 4 × 24
= 6 × 16
= 8 × 12
素数一覧
中学受験生は以下の素数を覚えよう。
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97
