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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 28 |
| 5 | 280 |
| 6 | 3486 |
| 7 | 50624 |
| 8 | 877080 |
| 9 | 17677440 |
| 10 | 404537050 |
| 11 | 10360548352 |
| 12 | 293676213876 |
| 13 | 9126971869184 |
| 14 | 308568877413174 |
| 15 | 11274243944693760 |
| 16 | 442681525701106096 |
| 17 | 18588860836606935040 |
| 18 | 831243363178769061426 |
| 19 | 39436124829328468606976 |
| 20 | 1978382154057910059275340 |
[0,0,2,6,28,280,3486,50624,877080,17677440, 404537050,10360548352,293676213876,9126971869184, 308568877413174,11274243944693760, 442681525701106096,18588860836606935040, 831243363178769061426,39436124829328468606976, 1978382154057910059275340] |