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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 6 |
| 4 | 36 |
| 5 | 231 |
| 6 | 1386 |
| 7 | 8496 |
| 8 | 50976 |
| 9 | 306956 |
| 10 | 1842276 |
| 11 | 11060586 |
| 12 | 66363516 |
| 13 | 398229516 |
| 14 | 2389377096 |
| 15 | 14336517456 |
| 16 | 86019146316 |
| 17 | 516116428791 |
| 18 | 3096698572746 |
| 19 | 18580200896796 |
| 20 | 111481205380776 |
| 21 | 668887287816276 |
[1,1,6,36,231,1386,8496,50976,306956,1842276, 11060586,66363516,398229516,2389377096, 14336517456,86019146316,516116428791, 3096698572746,18580200896796,111481205380776, 668887287816276] |