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| n | a(n) |
|---|---|
| 2 | 1 |
| 3 | 3 |
| 4 | 18 |
| 5 | 210 |
| 6 | 2565 |
| 7 | 32193 |
| 8 | 299299 |
| 9 | 2161092 |
| 10 | 14903940 |
| 11 | 101124595 |
| 12 | 666560697 |
| 13 | 4246100664 |
| 14 | 25977358680 |
| 15 | 152079371640 |
| 16 | 852145833870 |
| 17 | 4596664464916 |
| 18 | 24033240110143 |
| 19 | 122242188808411 |
| 20 | 605721155611160 |
| 21 | 2925464857935060 |
[1,3,18,210,2565,32193,299299,2161092,14903940, 101124595,666560697,4246100664,25977358680, 152079371640,852145833870,4596664464916, 24033240110143,122242188808411,605721155611160, 2925464857935060] |