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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 24 |
| 5 | 198 |
| 6 | 2110 |
| 7 | 27768 |
| 8 | 436656 |
| 9 | 8003950 |
| 10 | 167779068 |
| 11 | 3961727820 |
| 12 | 104102329504 |
| 13 | 3013887239454 |
| 14 | 95338047836520 |
| 15 | 3272043459321328 |
| 16 | 121106541865151040 |
| 17 | 4808924948167249302 |
| 18 | 203931444227955436816 |
| 19 | 9198925314402386788500 |
| 20 | 439809753701222702598528 |
[0,0,1,4,24,198,2110,27768,436656,8003950, 167779068,3961727820,104102329504,3013887239454, 95338047836520,3272043459321328, 121106541865151040,4808924948167249302, 203931444227955436816,9198925314402386788500, 439809753701222702598528] |