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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 9 |
| 3 | 77 |
| 4 | 694 |
| 5 | 6774 |
| 6 | 71820 |
| 7 | 826020 |
| 8 | 10265040 |
| 9 | 137275920 |
| 10 | 1967222880 |
| 11 | 30092580000 |
| 12 | 489584390400 |
| 13 | 8443643040000 |
| 14 | 153903497126400 |
| 15 | 2956596769728000 |
| 16 | 59712542813952000 |
| 17 | 1264947863784192000 |
| 18 | 28047600771531264000 |
| 19 | 649672514944814592000 |
| 20 | 15692497566512836608000 |
| 21 | 394613964462556016640000 |
[1,9,77,694,6774,71820,826020,10265040,137275920, 1967222880,30092580000,489584390400,8443643040000, 153903497126400,2956596769728000, 59712542813952000,1264947863784192000, 28047600771531264000,649672514944814592000, 15692497566512836608000,394613964462556016640000] |