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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 5 |
| 5 | 20 |
| 6 | 115 |
| 7 | 790 |
| 8 | 6217 |
| 9 | 55160 |
| 10 | 545135 |
| 11 | 5938490 |
| 12 | 70686805 |
| 13 | 912660508 |
| 14 | 12702694075 |
| 15 | 189579135710 |
| 16 | 3019908731105 |
| 17 | 51139445487680 |
| 18 | 917345570926087 |
| 19 | 17376071107513090 |
| 20 | 346563420097249645 |
| 21 | 7259714390232227300 |
| 22 | 159352909727731210835 |
| 23 | 3657569576966074846118 |
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