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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 31 |
| 5 | 348 |
| 6 | 5042 |
| 7 | 88688 |
| 8 | 1824547 |
| 9 | 42820188 |
| 10 | 1126268086 |
| 11 | 32763077560 |
| 12 | 1043332897134 |
| 13 | 36074556857688 |
| 14 | 1345273816275396 |
| 15 | 53805147477433032 |
| 16 | 2297089670073393203 |
| 17 | 104254628953344306652 |
| 18 | 5012154610038856594222 |
| 19 | 254446503765279301626680 |
| 20 | 13601683265701053731130458 |
| 21 | 763693471378260675464295240 |
[1,1,1,4,31,348,5042,88688,1824547,42820188, 1126268086,32763077560,1043332897134, 36074556857688,1345273816275396,53805147477433032, 2297089670073393203,104254628953344306652, 5012154610038856594222,254446503765279301626680, 13601683265701053731130458, 763693471378260675464295240] |