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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 9 |
| 5 | 45 |
| 6 | 225 |
| 7 | 1071 |
| 8 | 6993 |
| 9 | 56697 |
| 10 | 467745 |
| 11 | 3279419 |
| 12 | 29529753 |
| 13 | 376156261 |
| 14 | 4297350785 |
| 15 | 35274762407 |
| 16 | 378759492257 |
| 17 | 8003761282417 |
| 18 | 122599030798017 |
| 19 | 853554115621363 |
| 20 | 8002975063348265 |
| 21 | 450081179390735645 |
[1,1,1,3,9,45,225,1071,6993,56697,467745,3279419, 29529753,376156261,4297350785,35274762407, 378759492257,8003761282417,122599030798017, 853554115621363,8002975063348265, 450081179390735645] |