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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 8 |
| 3 | 51 |
| 4 | 304 |
| 5 | 1765 |
| 6 | 10104 |
| 7 | 57239 |
| 8 | 321248 |
| 9 | 1787337 |
| 10 | 9864040 |
| 11 | 54035707 |
| 12 | 294031632 |
| 13 | 1590368429 |
| 14 | 8556082136 |
| 15 | 45812239455 |
| 16 | 244255416256 |
| 17 | 1297362967441 |
| 18 | 6867617339592 |
| 19 | 36243304518083 |
| 20 | 190746485895920 |
| 21 | 1001394643462773 |
[0,1,8,51,304,1765,10104,57239,321248,1787337, 9864040,54035707,294031632,1590368429,8556082136, 45812239455,244255416256,1297362967441, 6867617339592,36243304518083,190746485895920, 1001394643462773] |