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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 120 |
| 4 | 3030 |
| 5 | 24552 |
| 6 | 130740 |
| 7 | 551640 |
| 8 | 1997415 |
| 9 | 6470420 |
| 10 | 19219462 |
| 11 | 53187840 |
| 12 | 138658760 |
| 13 | 343297780 |
| 14 | 812249250 |
| 15 | 1845669776 |
| 16 | 4044119530 |
| 17 | 8573706300 |
| 18 | 17637474350 |
| 19 | 35294157340 |
| 20 | 68850086745 |
| 21 | 131179071560 |
| 22 | 244518601660 |
| 23 | 446576824800 |
| 24 | 800201972990 |
| 25 | 1408466719120 |
[0,0,120,3030,24552,130740,551640,1997415,6470420, 19219462,53187840,138658760,343297780,812249250, 1845669776,4044119530,8573706300,17637474350, 35294157340,68850086745,131179071560,244518601660, 446576824800,800201972990,1408466719120] |