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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 3 |
| 3 | 6 |
| 4 | 27 |
| 5 | 252 |
| 6 | 1125 |
| 7 | 10206 |
| 8 | 108297 |
| 9 | 811944 |
| 10 | 10272339 |
| 11 | 131572350 |
| 12 | 1410753267 |
| 13 | 22363938324 |
| 14 | 342373389813 |
| 15 | 4790641828518 |
| 16 | 90549635310225 |
| 17 | 1626834238205904 |
| 18 | 28073013793245603 |
| 19 | 614304628556766966 |
| 20 | 12727707975543382731 |
[1,0,3,6,27,252,1125,10206,108297,811944,10272339, 131572350,1410753267,22363938324,342373389813, 4790641828518,90549635310225,1626834238205904, 28073013793245603,614304628556766966, 12727707975543382731] |