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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 22 |
| 5 | 100 |
| 6 | 1350 |
| 7 | 9744 |
| 8 | 162456 |
| 9 | 1614816 |
| 10 | 32319000 |
| 11 | 410031600 |
| 12 | 9604465200 |
| 13 | 148370508000 |
| 14 | 3986353491120 |
| 15 | 72622987557120 |
| 16 | 2202727143576960 |
| 17 | 46243059751848960 |
| 18 | 1563325251963995520 |
| 19 | 37165349757066935040 |
| 20 | 1385918755006365216000 |
| 21 | 36804377751967949760000 |
[1,0,1,2,22,100,1350,9744,162456,1614816,32319000, 410031600,9604465200,148370508000,3986353491120, 72622987557120,2202727143576960,46243059751848960, 1563325251963995520,37165349757066935040, 1385918755006365216000,36804377751967949760000] |