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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 73 |
| 5 | 283 |
| 6 | 1142 |
| 7 | 4755 |
| 8 | 20265 |
| 9 | 88008 |
| 10 | 388019 |
| 11 | 1732149 |
| 12 | 7813150 |
| 13 | 35552366 |
| 14 | 162990372 |
| 15 | 752066174 |
| 16 | 3489693468 |
| 17 | 16272504647 |
| 18 | 76209077491 |
| 19 | 358289119715 |
| 20 | 1690271229450 |
| 21 | 7998758682268 |
| 22 | 37957799055769 |
| 23 | 180583561604053 |
| 24 | 861103635616171 |
| 25 | 4114776349709555 |
| 26 | 19700383492079739 |
| 27 | 94487342382880327 |
[1,2,6,20,73,283,1142,4755,20265,88008,388019, 1732149,7813150,35552366,162990372,752066174, 3489693468,16272504647,76209077491,358289119715, 1690271229450,7998758682268,37957799055769, 180583561604053,861103635616171,4114776349709555, 19700383492079739,94487342382880327] |