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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 15 |
| 5 | 82 |
| 6 | 402 |
| 7 | 2352 |
| 8 | 22113 |
| 9 | 220504 |
| 10 | 2329650 |
| 11 | 26780256 |
| 12 | 293266680 |
| 13 | 3505934160 |
| 14 | 45390355920 |
| 15 | 633293015040 |
| 16 | 10873520709273 |
| 17 | 195823830637744 |
| 18 | 3698406245739330 |
| 19 | 73192513664010816 |
| 20 | 1509611621730135000 |
| 21 | 32576548307761013760 |
| 22 | 734272503865161846480 |
[0,0,1,2,15,82,402,2352,22113,220504,2329650, 26780256,293266680,3505934160,45390355920, 633293015040,10873520709273,195823830637744, 3698406245739330,73192513664010816, 1509611621730135000,32576548307761013760, 734272503865161846480] |