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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 37 |
| 5 | 112 |
| 6 | 336 |
| 7 | 1009 |
| 8 | 3028 |
| 9 | 9084 |
| 10 | 27253 |
| 11 | 81760 |
| 12 | 245280 |
| 13 | 735841 |
| 14 | 2207524 |
| 15 | 6622572 |
| 16 | 19867717 |
| 17 | 59603152 |
| 18 | 178809456 |
| 19 | 536428369 |
| 20 | 1609285108 |
| 21 | 4827855324 |
| 22 | 14483565973 |
| 23 | 43450697920 |
| 24 | 130352093760 |
| 25 | 391056281281 |
| 26 | 1173168843844 |
| 27 | 3519506531532 |
| 28 | 10558519594597 |
[1,4,12,37,112,336,1009,3028,9084,27253,81760, 245280,735841,2207524,6622572,19867717,59603152, 178809456,536428369,1609285108,4827855324, 14483565973,43450697920,130352093760,391056281281, 1173168843844,3519506531532,10558519594597] |