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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 33 |
| 4 | 384 |
| 5 | 5705 |
| 6 | 103392 |
| 7 | 2213225 |
| 8 | 54648832 |
| 9 | 1529006769 |
| 10 | 47806489600 |
| 11 | 1651929898641 |
| 12 | 62514008358912 |
| 13 | 2571311967708601 |
| 14 | 114219516618117120 |
| 15 | 5449390043986849305 |
| 16 | 277913379747357786112 |
| 17 | 15087434965491213149153 |
| 18 | 868698417435317196816384 |
| 19 | 52875073161897308106963585 |
[1,1,4,33,384,5705,103392,2213225,54648832, 1529006769,47806489600,1651929898641, 62514008358912,2571311967708601, 114219516618117120,5449390043986849305, 277913379747357786112,15087434965491213149153, 868698417435317196816384, 52875073161897308106963585] |