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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 28 |
| 4 | 292 |
| 5 | 4408 |
| 6 | 97432 |
| 7 | 3231256 |
| 8 | 164789104 |
| 9 | 13170099856 |
| 10 | 1670220282544 |
| 11 | 338692348412320 |
| 12 | 110327835695333920 |
| 13 | 57892877044109184160 |
| 14 | 49019180876700301391680 |
| 15 | 67044425508546158335526080 |
| 16 | 148216012413625321252632612160 |
| 17 | 529829556146109541834263919553920 |
[1,1,4,28,292,4408,97432,3231256,164789104, 13170099856,1670220282544,338692348412320, 110327835695333920,57892877044109184160, 49019180876700301391680, 67044425508546158335526080, 148216012413625321252632612160, 529829556146109541834263919553920] |