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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 72 |
| 5 | 780 |
| 6 | 8520 |
| 7 | 97650 |
| 8 | 1189104 |
| 9 | 15441048 |
| 10 | 213816240 |
| 11 | 3152287710 |
| 12 | 49369524600 |
| 13 | 819340272036 |
| 14 | 14373198453432 |
| 15 | 265869427695690 |
| 16 | 5173710021214560 |
| 17 | 105683257864542000 |
| 18 | 2261482144869433824 |
| 19 | 50598160483438733238 |
| 20 | 1181568482279829616680 |
| 21 | 28750554997809594831420 |
[0,0,0,6,72,780,8520,97650,1189104,15441048, 213816240,3152287710,49369524600,819340272036, 14373198453432,265869427695690,5173710021214560, 105683257864542000,2261482144869433824, 50598160483438733238,1181568482279829616680, 28750554997809594831420] |