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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 20 |
| 4 | 280 |
| 5 | 280 |
| 6 | 3080 |
| 7 | 5720 |
| 8 | 2288 |
| 9 | 116688 |
| 10 | 3695120 |
| 11 | 25865840 |
| 12 | 594914320 |
| 13 | 2974571600 |
| 14 | 8923714800 |
| 15 | 86262576400 |
| 16 | 5348279736800 |
| 17 | 5348279736800 |
| 18 | 16044839210400 |
| 19 | 197886350261600 |
| 20 | 15222026943200 |
| 21 | 89157586381600 |
[2,4,20,280,280,3080,5720,2288,116688,3695120, 25865840,594914320,2974571600,8923714800, 86262576400,5348279736800,5348279736800, 16044839210400,197886350261600,15222026943200, 89157586381600] |