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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 9 |
| 3 | 54 |
| 4 | 372 |
| 5 | 2778 |
| 6 | 21873 |
| 7 | 178786 |
| 8 | 1502649 |
| 9 | 12904524 |
| 10 | 112741664 |
| 11 | 998871030 |
| 12 | 8953443276 |
| 13 | 81047485148 |
| 14 | 739846170864 |
| 15 | 6803054508702 |
| 16 | 62954736555836 |
| 17 | 585850907166084 |
| 18 | 5479077065774682 |
| 19 | 51470699845616004 |
| 20 | 485456696541512442 |
| 21 | 4595280949098247422 |
[1,2,9,54,372,2778,21873,178786,1502649,12904524, 112741664,998871030,8953443276,81047485148, 739846170864,6803054508702,62954736555836, 585850907166084,5479077065774682, 51470699845616004,485456696541512442, 4595280949098247422] |