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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 4 |
| 4 | 10 |
| 5 | 40 |
| 6 | 230 |
| 7 | 1580 |
| 8 | 12434 |
| 9 | 110320 |
| 10 | 1090270 |
| 11 | 11876980 |
| 12 | 141373610 |
| 13 | 1825321016 |
| 14 | 25405388150 |
| 15 | 379158271420 |
| 16 | 6039817462210 |
| 17 | 102278890975360 |
| 18 | 1834691141852174 |
| 19 | 34752142215026180 |
| 20 | 693126840194499290 |
| 21 | 14519428780464454600 |
| 22 | 318705819455462421670 |
[0,0,2,4,10,40,230,1580,12434,110320,1090270, 11876980,141373610,1825321016,25405388150, 379158271420,6039817462210,102278890975360, 1834691141852174,34752142215026180, 693126840194499290,14519428780464454600, 318705819455462421670] |