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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 21 |
| 4 | 146 |
| 5 | 1240 |
| 6 | 12479 |
| 7 | 144970 |
| 8 | 1908682 |
| 9 | 28079550 |
| 10 | 456458832 |
| 11 | 8125189974 |
| 12 | 157190542607 |
| 13 | 3284222304545 |
| 14 | 73705849847317 |
| 15 | 1768479436456975 |
| 16 | 45180024672023814 |
| 17 | 1224529894981726614 |
| 18 | 35096983241255523572 |
| 19 | 1060703070504583747430 |
| 20 | 33714045363258013414692 |
[1,1,4,21,146,1240,12479,144970,1908682,28079550, 456458832,8125189974,157190542607,3284222304545, 73705849847317,1768479436456975,45180024672023814, 1224529894981726614,35096983241255523572, 1060703070504583747430,33714045363258013414692] |