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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 69 |
| 4 | 1200 |
| 5 | 28085 |
| 6 | 828240 |
| 7 | 29502473 |
| 8 | 1232606592 |
| 9 | 59114482569 |
| 10 | 3201204188160 |
| 11 | 193215861134989 |
| 12 | 12862437022076928 |
| 13 | 936256855741871677 |
| 14 | 73978404781917941760 |
| 15 | 6306254322850544942865 |
| 16 | 576881179288397985054720 |
| 17 | 56369243043268551691136657 |
| 18 | 5859726074013471622734938112 |
[1,1,6,69,1200,28085,828240,29502473,1232606592, 59114482569,3201204188160,193215861134989, 12862437022076928,936256855741871677, 73978404781917941760,6306254322850544942865, 576881179288397985054720, 56369243043268551691136657, 5859726074013471622734938112] |