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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 28 |
| 5 | 210 |
| 6 | 1248 |
| 7 | 13020 |
| 8 | 102128 |
| 9 | 1248912 |
| 10 | 13457880 |
| 11 | 176726880 |
| 12 | 2362784928 |
| 13 | 36609693120 |
| 14 | 551337892896 |
| 15 | 9588702417840 |
| 16 | 171779733546240 |
| 17 | 3230529997766400 |
| 18 | 64714946343904512 |
| 19 | 1371420774325866240 |
| 20 | 29953522454811096960 |
| 21 | 698447624328756610560 |
[1,0,2,6,28,210,1248,13020,102128,1248912, 13457880,176726880,2362784928,36609693120, 551337892896,9588702417840,171779733546240, 3230529997766400,64714946343904512, 1371420774325866240,29953522454811096960, 698447624328756610560] |