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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 7 |
| 3 | 56 |
| 4 | 413 |
| 5 | 3108 |
| 6 | 23163 |
| 7 | 172711 |
| 8 | 1285256 |
| 9 | 9556603 |
| 10 | 70980000 |
| 11 | 526711507 |
| 12 | 3904946864 |
| 13 | 28926003505 |
| 14 | 214095348671 |
| 15 | 1583389916081 |
| 16 | 11701578676851 |
| 17 | 86415267247743 |
| 18 | 637732279701496 |
| 19 | 4703270177738076 |
| 20 | 34664585073280204 |
| 21 | 255332979654402524 |
| 22 | 1879629724498860397 |
| 23 | 13829015594546304600 |
[1,1,7,56,413,3108,23163,172711,1285256,9556603, 70980000,526711507,3904946864,28926003505, 214095348671,1583389916081,11701578676851, 86415267247743,637732279701496,4703270177738076, 34664585073280204,255332979654402524, 1879629724498860397,13829015594546304600] |