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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 142 |
| 5 | 1540 |
| 6 | 40028 |
| 7 | 830088 |
| 8 | 26194320 |
| 9 | 803816928 |
| 10 | 30965575632 |
| 11 | 1243606193280 |
| 12 | 57518659025232 |
| 13 | 2831567070616128 |
| 14 | 154016101401783840 |
| 15 | 8940598021282475520 |
| 16 | 561024734955178219392 |
| 17 | 37443206368654913645568 |
| 18 | 2666651445545095799647488 |
| 19 | 200981356103135218506923520 |
[1,0,2,6,142,1540,40028,830088,26194320,803816928, 30965575632,1243606193280,57518659025232, 2831567070616128,154016101401783840, 8940598021282475520,561024734955178219392, 37443206368654913645568,2666651445545095799647488, 200981356103135218506923520] |