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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 48 |
| 5 | 305 |
| 6 | 2280 |
| 7 | 19537 |
| 8 | 188608 |
| 9 | 2024577 |
| 10 | 23911200 |
| 11 | 308049401 |
| 12 | 4298093184 |
| 13 | 64555255921 |
| 14 | 1038311141504 |
| 15 | 17803434637185 |
| 16 | 324148992092160 |
| 17 | 6245040776838017 |
| 18 | 126919440612205056 |
| 19 | 2713418986517310313 |
| 20 | 60871624993766717440 |
| 21 | 1429679116231319002161 |
[1,1,2,9,48,305,2280,19537,188608,2024577, 23911200,308049401,4298093184,64555255921, 1038311141504,17803434637185,324148992092160, 6245040776838017,126919440612205056, 2713418986517310313,60871624993766717440, 1429679116231319002161] |