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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 26 |
| 3 | 184 |
| 4 | 1316 |
| 5 | 9424 |
| 6 | 67496 |
| 7 | 483424 |
| 8 | 3462416 |
| 9 | 24798784 |
| 10 | 177615776 |
| 11 | 1272133504 |
| 12 | 9111373376 |
| 13 | 65258185984 |
| 14 | 467397247616 |
| 15 | 3347628865024 |
| 16 | 23976647434496 |
| 17 | 171727406285824 |
| 18 | 1229959365679616 |
| 19 | 8809310487721984 |
[1,4,26,184,1316,9424,67496,483424,3462416, 24798784,177615776,1272133504,9111373376, 65258185984,467397247616,3347628865024, 23976647434496,171727406285824,1229959365679616, 8809310487721984] |