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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 20 |
| 3 | 186 |
| 4 | 2272 |
| 5 | 34452 |
| 6 | 624680 |
| 7 | 13187184 |
| 8 | 317741776 |
| 9 | 8605402320 |
| 10 | 258797553152 |
| 11 | 8557530058656 |
| 12 | 308588677217920 |
| 13 | 12052073471616192 |
| 14 | 506804263162315904 |
| 15 | 22830295989247448064 |
| 16 | 1096867816010202138880 |
| 17 | 55985919208498803979008 |
[1,3,20,186,2272,34452,624680,13187184,317741776, 8605402320,258797553152,8557530058656, 308588677217920,12052073471616192, 506804263162315904,22830295989247448064, 1096867816010202138880,55985919208498803979008] |