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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 4 |
| 5 | 12 |
| 6 | 24 |
| 7 | 88 |
| 8 | 224 |
| 9 | 720 |
| 10 | 1792 |
| 11 | 7200 |
| 12 | 16512 |
| 13 | 69952 |
| 14 | 185984 |
| 15 | 608896 |
| 16 | 1797120 |
| 17 | 7495424 |
| 18 | 17936896 |
| 19 | 79457792 |
| 20 | 211576832 |
| 21 | 742306816 |
| 22 | 2190231552 |
| 23 | 9482688512 |
| 24 | 23198867456 |
| 25 | 97967427584 |
| 26 | 285227057152 |
| 27 | 1046412681216 |
| 28 | 3019819909120 |
[1,1,2,4,12,24,88,224,720,1792,7200,16512,69952, 185984,608896,1797120,7495424,17936896,79457792, 211576832,742306816,2190231552,9482688512, 23198867456,97967427584,285227057152, 1046412681216,3019819909120] |