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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 6 |
| 5 | 25 |
| 6 | 140 |
| 7 | 1561 |
| 8 | 19586 |
| 9 | 228425 |
| 10 | 2870160 |
| 11 | 44172601 |
| 12 | 780614846 |
| 13 | 14499946825 |
| 14 | 284310704860 |
| 15 | 6089231941521 |
| 16 | 142225796401786 |
| 17 | 3537029819020905 |
| 18 | 92766573133851240 |
| 19 | 2577870903366020521 |
| 20 | 75999605064376599606 |
| 21 | 2362944241092314079145 |
[1,0,0,1,6,25,140,1561,19586,228425,2870160, 44172601,780614846,14499946825,284310704860, 6089231941521,142225796401786,3537029819020905, 92766573133851240,2577870903366020521, 75999605064376599606,2362944241092314079145] |