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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 18 |
| 4 | 166 |
| 5 | 1720 |
| 6 | 20168 |
| 7 | 265776 |
| 8 | 3900048 |
| 9 | 63160944 |
| 10 | 1119902112 |
| 11 | 21588456912 |
| 12 | 449695165104 |
| 13 | 10068121989120 |
| 14 | 241142216363904 |
| 15 | 6153066311872128 |
| 16 | 166649425520796288 |
| 17 | 4775084999073669888 |
| 18 | 144324648624594398976 |
| 19 | 4589066547251186277888 |
[0,0,2,18,166,1720,20168,265776,3900048,63160944, 1119902112,21588456912,449695165104, 10068121989120,241142216363904,6153066311872128, 166649425520796288,4775084999073669888, 144324648624594398976,4589066547251186277888] |