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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 18 |
| 3 | 135 |
| 4 | 796 |
| 5 | 4605 |
| 6 | 28926 |
| 7 | 204883 |
| 8 | 1643160 |
| 9 | 14795001 |
| 10 | 147960010 |
| 11 | 1627574751 |
| 12 | 19530917748 |
| 13 | 253901959285 |
| 14 | 3554627468406 |
| 15 | 53319412076715 |
| 16 | 853110593292976 |
| 17 | 14502880086064113 |
| 18 | 261051841549259010 |
| 19 | 4959984989436051511 |
| 20 | 99199699788721190220 |
[0,1,18,135,796,4605,28926,204883,1643160, 14795001,147960010,1627574751,19530917748, 253901959285,3554627468406,53319412076715, 853110593292976,14502880086064113, 261051841549259010,4959984989436051511, 99199699788721190220] |