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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 5 |
| 5 | 19 |
| 6 | 110 |
| 7 | 975 |
| 8 | 13555 |
| 9 | 297330 |
| 10 | 10393875 |
| 11 | 581772345 |
| 12 | 52349401830 |
| 13 | 7590091602225 |
| 14 | 1776029657181945 |
| 15 | 671331672100911690 |
| 16 | 410181883162313724165 |
| 17 | 405259031001185201881755 |
| 18 | 647603522027573971050913590 |
| 19 | 1674054699591760033962965879295 |
[1,1,1,2,5,19,110,975,13555,297330,10393875, 581772345,52349401830,7590091602225, 1776029657181945,671331672100911690, 410181883162313724165,405259031001185201881755, 647603522027573971050913590, 1674054699591760033962965879295] |