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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 3 |
| 3 | 23 |
| 4 | 278 |
| 5 | 4624 |
| 6 | 98064 |
| 7 | 2530142 |
| 8 | 76931224 |
| 9 | 2694025872 |
| 10 | 106782582720 |
| 11 | 4726084696992 |
| 12 | 231030209532528 |
| 13 | 12362764041338736 |
| 14 | 718779255989466840 |
| 15 | 45118706229328822680 |
| 16 | 3041140847160686156544 |
| 17 | 219071239142209684437504 |
| 18 | 16796070771249534388114176 |
[0,1,3,23,278,4624,98064,2530142,76931224, 2694025872,106782582720,4726084696992, 231030209532528,12362764041338736, 718779255989466840,45118706229328822680, 3041140847160686156544,219071239142209684437504, 16796070771249534388114176] |