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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 24 |
| 3 | 112 |
| 4 | 528 |
| 5 | 2301 |
| 6 | 10237 |
| 7 | 42757 |
| 8 | 171744 |
| 9 | 691217 |
| 10 | 2781996 |
| 11 | 11116745 |
| 12 | 44545473 |
| 13 | 178217816 |
| 14 | 713157656 |
| 15 | 2852582716 |
[1,4,24,112,528,2301,10237,42757,171744,691217, 2781996,11116745,44545473,178217816,713157656, 2852582716] |