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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 68 |
| 5 | 646 |
| 6 | 6857 |
| 7 | 77695 |
| 8 | 919642 |
| 9 | 11233858 |
| 10 | 140544189 |
| 11 | 1791614714 |
| 12 | 23187320736 |
| 13 | 303861373679 |
| 14 | 4023883823059 |
| 15 | 53762917329659 |
| 16 | 723854999871943 |
| 17 | 9811154512175468 |
| 18 | 133762940465746744 |
| 19 | 1833187046654598058 |
| 20 | 25239961633188882896 |
[1,1,2,9,68,646,6857,77695,919642,11233858, 140544189,1791614714,23187320736,303861373679, 4023883823059,53762917329659,723854999871943, 9811154512175468,133762940465746744, 1833187046654598058,25239961633188882896] |