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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 3 |
| 3 | 12 |
| 4 | 53 |
| 5 | 282 |
| 6 | 1753 |
| 7 | 12566 |
| 8 | 102233 |
| 9 | 931746 |
| 10 | 9408941 |
| 11 | 104310042 |
| 12 | 1259745925 |
| 13 | 16464164978 |
| 14 | 231539899697 |
| 15 | 3486551697582 |
| 16 | 55972130401073 |
| 17 | 954322312212546 |
| 18 | 17222351842894933 |
| 19 | 327979242711784226 |
| 20 | 6573122342554664381 |
| 21 | 138292026914011788882 |
[0,1,3,12,53,282,1753,12566,102233,931746,9408941, 104310042,1259745925,16464164978,231539899697, 3486551697582,55972130401073,954322312212546, 17222351842894933,327979242711784226, 6573122342554664381,138292026914011788882] |