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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 25 |
| 4 | 181 |
| 5 | 1399 |
| 6 | 11212 |
| 7 | 91936 |
| 8 | 765805 |
| 9 | 6452449 |
| 10 | 54841438 |
| 11 | 469306102 |
| 12 | 4038193870 |
| 13 | 34903997029 |
| 14 | 302828905471 |
| 15 | 2635745917759 |
| 16 | 23003622046900 |
| 17 | 201241080558652 |
| 18 | 1764149626139119 |
| 19 | 15493365042402772 |
| 20 | 136288275628625410 |
| 21 | 1200600389345625754 |
[1,1,4,25,181,1399,11212,91936,765805,6452449, 54841438,469306102,4038193870,34903997029, 302828905471,2635745917759,23003622046900, 201241080558652,1764149626139119, 15493365042402772,136288275628625410, 1200600389345625754] |