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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 6 |
| 3 | 24 |
| 4 | 102 |
| 5 | 516 |
| 6 | 2814 |
| 7 | 16752 |
| 8 | 106026 |
| 9 | 712260 |
| 10 | 5027190 |
| 11 | 37158600 |
| 12 | 286141638 |
| 13 | 2289018708 |
| 14 | 18961164774 |
| 15 | 162271001760 |
| 16 | 1431533922642 |
| 17 | 12994777356228 |
| 18 | 121174578691398 |
| 19 | 1159065402957240 |
| 20 | 11357543381281638 |
| 21 | 113876839666712676 |
[1,3,6,24,102,516,2814,16752,106026,712260, 5027190,37158600,286141638,2289018708,18961164774, 162271001760,1431533922642,12994777356228, 121174578691398,1159065402957240, 11357543381281638,113876839666712676] |