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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 13 |
| 5 | 73 |
| 6 | 505 |
| 7 | 4143 |
| 8 | 39313 |
| 9 | 423401 |
| 10 | 5101785 |
| 11 | 67994611 |
| 12 | 993048765 |
| 13 | 15770916657 |
| 14 | 270586214481 |
| 15 | 4987678532991 |
| 16 | 98297729816321 |
| 17 | 2062591323728689 |
| 18 | 45908909743929681 |
| 19 | 1080350557160580163 |
| 20 | 26800186367114537613 |
| 21 | 698982753383076195897 |
[1,1,1,3,13,73,505,4143,39313,423401,5101785, 67994611,993048765,15770916657,270586214481, 4987678532991,98297729816321,2062591323728689, 45908909743929681,1080350557160580163, 26800186367114537613,698982753383076195897] |