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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 12 |
| 4 | 64 |
| 5 | 350 |
| 6 | 2024 |
| 7 | 12460 |
| 8 | 81638 |
| 9 | 567888 |
| 10 | 4180848 |
| 11 | 32470834 |
| 12 | 265219332 |
| 13 | 2271692124 |
| 14 | 20350705418 |
| 15 | 190216812260 |
| 16 | 1850993707960 |
| 17 | 18714559108142 |
| 18 | 196237054861920 |
| 19 | 2130518566431620 |
| 20 | 23912733627261670 |
| 21 | 277078872201375976 |
| 22 | 3310142647325149512 |
[0,0,2,12,64,350,2024,12460,81638,567888,4180848, 32470834,265219332,2271692124,20350705418, 190216812260,1850993707960,18714559108142, 196237054861920,2130518566431620, 23912733627261670,277078872201375976, 3310142647325149512] |