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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 56 |
| 5 | 480 |
| 6 | 5094 |
| 7 | 65534 |
| 8 | 984808 |
| 9 | 16992144 |
| 10 | 330667680 |
| 11 | 7130797872 |
| 12 | 168564160632 |
| 13 | 4321664793264 |
| 14 | 119356965323400 |
| 15 | 3528831476247240 |
| 16 | 111173720474673984 |
| 17 | 3716755785886791168 |
| 18 | 131414199676568655552 |
| 19 | 4899052003032070987968 |
| 20 | 192050612714621129114880 |
[1,1,2,9,56,480,5094,65534,984808,16992144, 330667680,7130797872,168564160632,4321664793264, 119356965323400,3528831476247240, 111173720474673984,3716755785886791168, 131414199676568655552,4899052003032070987968, 192050612714621129114880] |