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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 25 |
| 5 | 135 |
| 6 | 909 |
| 7 | 7417 |
| 8 | 71698 |
| 9 | 806968 |
| 10 | 10427825 |
| 11 | 152915697 |
| 12 | 2519879761 |
| 13 | 46276398129 |
| 14 | 940296067422 |
| 15 | 21007099850230 |
| 16 | 513172107841525 |
| 17 | 13640345170943527 |
| 18 | 392780078386164389 |
| 19 | 12204609567437300313 |
| 20 | 407757149671568266678 |
| 21 | 14600807659376773500696 |
[1,1,2,6,25,135,909,7417,71698,806968,10427825, 152915697,2519879761,46276398129,940296067422, 21007099850230,513172107841525,13640345170943527, 392780078386164389,12204609567437300313, 407757149671568266678,14600807659376773500696] |