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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 15 |
| 4 | 112 |
| 5 | 925 |
| 6 | 8556 |
| 7 | 88249 |
| 8 | 1007056 |
| 9 | 12612681 |
| 10 | 172092340 |
| 11 | 2541367741 |
| 12 | 40385290584 |
| 13 | 687120886621 |
| 14 | 12461362029676 |
| 15 | 239945693311185 |
| 16 | 4888311943969696 |
| 17 | 105038684764873489 |
| 18 | 2373935421890157156 |
| 19 | 56288808913905658981 |
| 20 | 1397063652149884343080 |
| 21 | 36219993180755369947941 |
[0,0,2,15,112,925,8556,88249,1007056,12612681, 172092340,2541367741,40385290584,687120886621, 12461362029676,239945693311185,4888311943969696, 105038684764873489,2373935421890157156, 56288808913905658981,1397063652149884343080, 36219993180755369947941] |