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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 10 |
| 3 | 44 |
| 4 | 228 |
| 5 | 1272 |
| 6 | 8760 |
| 7 | 63936 |
| 8 | 547776 |
| 9 | 5145984 |
| 10 | 54233280 |
| 11 | 624291840 |
| 12 | 7879472640 |
| 13 | 107423677440 |
| 14 | 1579212910080 |
| 15 | 24832164556800 |
| 16 | 416273901926400 |
| 17 | 7403098797158400 |
| 18 | 139238590721126400 |
| 19 | 2760253302701260800 |
| 20 | 57522218527420416000 |
| 21 | 1256931901812400128000 |
[1,2,10,44,228,1272,8760,63936,547776,5145984, 54233280,624291840,7879472640,107423677440, 1579212910080,24832164556800,416273901926400, 7403098797158400,139238590721126400, 2760253302701260800,57522218527420416000, 1256931901812400128000] |