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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 6 |
| 3 | 30 |
| 4 | 120 |
| 5 | 420 |
| 6 | 1344 |
| 7 | 4032 |
| 8 | 11520 |
| 9 | 31680 |
| 10 | 84480 |
| 11 | 219648 |
| 12 | 559104 |
| 13 | 1397760 |
| 14 | 3440640 |
| 15 | 8355840 |
| 16 | 20054016 |
| 17 | 47628288 |
| 18 | 112066560 |
| 19 | 261488640 |
| 20 | 605552640 |
| 21 | 1392771072 |
| 22 | 3183476736 |
| 23 | 7235174400 |
| 24 | 16357785600 |
| 25 | 36805017600 |
| 26 | 82443239424 |
| 27 | 183911841792 |
| 28 | 408692981760 |
| 29 | 904963031040 |
[0,1,6,30,120,420,1344,4032,11520,31680,84480, 219648,559104,1397760,3440640,8355840,20054016, 47628288,112066560,261488640,605552640,1392771072, 3183476736,7235174400,16357785600,36805017600, 82443239424,183911841792,408692981760, 904963031040] |