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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 60 |
| 5 | 485 |
| 6 | 4680 |
| 7 | 53557 |
| 8 | 709968 |
| 9 | 10662633 |
| 10 | 178786080 |
| 11 | 3312164801 |
| 12 | 67201649856 |
| 13 | 1481949570829 |
| 14 | 35291569832064 |
| 15 | 902631317654445 |
| 16 | 24676916031310080 |
| 17 | 718135040275928657 |
| 18 | 22164641043514532352 |
| 19 | 723163494821506484473 |
| 20 | 24869366907327781002240 |
[1,1,2,9,60,485,4680,53557,709968,10662633, 178786080,3312164801,67201649856,1481949570829, 35291569832064,902631317654445,24676916031310080, 718135040275928657,22164641043514532352, 723163494821506484473,24869366907327781002240] |