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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 3 |
| 3 | 20 |
| 4 | 220 |
| 5 | 3424 |
| 6 | 69008 |
| 7 | 1706256 |
| 8 | 49956240 |
| 9 | 1689497376 |
| 10 | 64799254752 |
| 11 | 2778906776832 |
| 12 | 131756614920192 |
| 13 | 6843405231815424 |
| 14 | 386414606189283072 |
| 15 | 23567401521343170048 |
| 16 | 1543994621969805135360 |
| 17 | 108137637714495023354880 |
| 18 | 8062825821198926369725440 |
[0,1,3,20,220,3424,69008,1706256,49956240, 1689497376,64799254752,2778906776832, 131756614920192,6843405231815424, 386414606189283072,23567401521343170048, 1543994621969805135360,108137637714495023354880, 8062825821198926369725440] |