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| n | a(n) |
|---|---|
| 2 | 1 |
| 3 | 0 |
| 4 | 6 |
| 5 | 20 |
| 6 | 120 |
| 7 | 672 |
| 8 | 5516 |
| 9 | 40140 |
| 10 | 368640 |
| 11 | 3521870 |
| 12 | 37445298 |
| 13 | 422339502 |
| 14 | 5215454426 |
| 15 | 68144100780 |
| 16 | 954428684280 |
| 17 | 14160968076584 |
| 18 | 222769496190060 |
| 19 | 3692874342747114 |
| 20 | 64493471050666430 |
| 21 | 1181830474135532130 |
| 22 | 22692074431844298558 |
| 23 | 455404848204906308984 |
[1,0,6,20,120,672,5516,40140,368640,3521870, 37445298,422339502,5215454426,68144100780, 954428684280,14160968076584,222769496190060, 3692874342747114,64493471050666430, 1181830474135532130,22692074431844298558, 455404848204906308984] |