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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 13 |
| 4 | 75 |
| 5 | 541 |
| 6 | 4683 |
| 7 | 47293 |
| 8 | 545835 |
| 9 | 6541426 |
| 10 | 82575992 |
| 11 | 1105638712 |
| 12 | 15740668640 |
| 13 | 238286993344 |
| 14 | 3830996668880 |
| 15 | 65290928665336 |
| 16 | 1177060804189460 |
| 17 | 22361980927148976 |
| 18 | 446348461695232608 |
| 19 | 9336784271669066016 |
| 20 | 204240575957464571232 |
| 21 | 4663193421334759826472 |
[1,1,3,13,75,541,4683,47293,545835,6541426, 82575992,1105638712,15740668640,238286993344, 3830996668880,65290928665336,1177060804189460, 22361980927148976,446348461695232608, 9336784271669066016,204240575957464571232, 4663193421334759826472] |