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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 15 |
| 4 | 79 |
| 5 | 468 |
| 6 | 2895 |
| 7 | 18670 |
| 8 | 123765 |
| 9 | 838860 |
| 10 | 5785503 |
| 11 | 40473729 |
| 12 | 286504086 |
| 13 | 2048388112 |
| 14 | 14770313397 |
| 15 | 107290913232 |
| 16 | 784380664232 |
| 17 | 5766985753620 |
| 18 | 42614014459911 |
| 19 | 316304429143995 |
| 20 | 2357275139670183 |
| 21 | 17631888703154172 |
[1,1,3,15,79,468,2895,18670,123765,838860,5785503, 40473729,286504086,2048388112,14770313397, 107290913232,784380664232,5766985753620, 42614014459911,316304429143995,2357275139670183, 17631888703154172] |