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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 12 |
| 5 | 54 |
| 6 | 432 |
| 7 | 2862 |
| 8 | 29880 |
| 9 | 311688 |
| 10 | 3530952 |
| 11 | 52947432 |
| 12 | 694960560 |
| 13 | 12339656640 |
| 14 | 208855024128 |
| 15 | 3885592056624 |
| 16 | 84031138091520 |
| 17 | 1688108258868480 |
| 18 | 41851910546369280 |
| 19 | 986544325475565696 |
| 20 | 25610732492679696384 |
| 21 | 720669291974958124800 |
| 22 | 19681263432530494848000 |
[1,1,1,3,12,54,432,2862,29880,311688,3530952, 52947432,694960560,12339656640,208855024128, 3885592056624,84031138091520,1688108258868480, 41851910546369280,986544325475565696, 25610732492679696384,720669291974958124800, 19681263432530494848000] |