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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 23 |
| 5 | 104 |
| 6 | 535 |
| 7 | 3081 |
| 8 | 19737 |
| 9 | 140454 |
| 10 | 1111136 |
| 11 | 9777465 |
| 12 | 95587370 |
| 13 | 1034517225 |
| 14 | 12324487009 |
| 15 | 160503772329 |
[1,1,2,6,23,104,535,3081,19737,140454,1111136, 9777465,95587370,1034517225,12324487009, 160503772329] |