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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 13 |
| 4 | 42 |
| 5 | 137 |
| 6 | 448 |
| 7 | 1465 |
| 8 | 4790 |
| 9 | 15661 |
| 10 | 51204 |
| 11 | 167413 |
| 12 | 547362 |
| 13 | 1789617 |
| 14 | 5851208 |
| 15 | 19130705 |
| 16 | 62548430 |
| 17 | 204504021 |
| 18 | 668632204 |
| 19 | 2186113613 |
| 20 | 7147565882 |
| 21 | 23369187097 |
| 22 | 76406277968 |
| 23 | 249812682345 |
| 24 | 816770269670 |
| 25 | 2670455587581 |
[0,1,4,13,42,137,448,1465,4790,15661,51204,167413, 547362,1789617,5851208,19130705,62548430, 204504021,668632204,2186113613,7147565882, 23369187097,76406277968,249812682345,816770269670, 2670455587581] |