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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 21 |
| 4 | 148 |
| 5 | 1305 |
| 6 | 13806 |
| 7 | 170401 |
| 8 | 2403640 |
| 9 | 38143377 |
| 10 | 672552730 |
| 11 | 13044463641 |
| 12 | 276003553860 |
| 13 | 6326524990825 |
| 14 | 156171026562838 |
| 15 | 4130464801497105 |
| 16 | 116526877671782896 |
| 17 | 3492868475952497313 |
| 18 | 110856698175372359346 |
| 19 | 3713836169709782989993 |
| 20 | 130966414749485504586940 |
[1,1,4,21,148,1305,13806,170401,2403640,38143377, 672552730,13044463641,276003553860,6326524990825, 156171026562838,4130464801497105, 116526877671782896,3492868475952497313, 110856698175372359346,3713836169709782989993, 130966414749485504586940] |