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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 8 |
| 4 | 41 |
| 5 | 252 |
| 6 | 1782 |
| 7 | 14121 |
| 8 | 123244 |
| 9 | 1169832 |
| 10 | 11960978 |
| 11 | 130742196 |
| 12 | 1518514076 |
| 13 | 18645970943 |
| 14 | 241030821566 |
| 15 | 3268214127548 |
| 16 | 46338504902485 |
| 17 | 685145875623056 |
| 18 | 10538790233183702 |
| 19 | 168282662416550040 |
| 20 | 2784205185437851772 |
| 21 | 47646587512911994120 |
[1,1,2,8,41,252,1782,14121,123244,1169832, 11960978,130742196,1518514076,18645970943, 241030821566,3268214127548,46338504902485, 685145875623056,10538790233183702, 168282662416550040,2784205185437851772, 47646587512911994120] |