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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 12 |
| 4 | 54 |
| 5 | 390 |
| 6 | 3120 |
| 7 | 28140 |
| 8 | 290640 |
| 9 | 3354960 |
| 10 | 42561120 |
| 11 | 586259520 |
| 12 | 8806422240 |
| 13 | 141680579040 |
| 14 | 2446025662080 |
| 15 | 44990666360640 |
| 16 | 877867974023040 |
| 17 | 18115179826423680 |
| 18 | 394351821275892480 |
| 19 | 9019730566889602560 |
[1,1,2,12,54,390,3120,28140,290640,3354960, 42561120,586259520,8806422240,141680579040, 2446025662080,44990666360640,877867974023040, 18115179826423680,394351821275892480, 9019730566889602560] |