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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 4 |
| 5 | 24 |
| 6 | 188 |
| 7 | 1705 |
| 8 | 16980 |
| 9 | 180670 |
| 10 | 2020120 |
| 11 | 23478426 |
| 12 | 281481880 |
| 13 | 3461873536 |
| 14 | 43494961404 |
| 15 | 556461656569 |
| 16 | 7230987646484 |
| 17 | 95244774132810 |
| 18 | 1269534571172912 |
| 19 | 17100621281619328 |
| 20 | 232511930087682528 |
| 21 | 3188042426888493288 |
[0,0,1,4,24,188,1705,16980,180670,2020120, 23478426,281481880,3461873536,43494961404, 556461656569,7230987646484,95244774132810, 1269534571172912,17100621281619328, 232511930087682528,3188042426888493288] |