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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 36 |
| 4 | 234 |
| 5 | 7290 |
| 6 | 54540 |
| 7 | 1408680 |
| 8 | 23119740 |
| 9 | 341788860 |
| 10 | 11790437400 |
| 11 | 231972879600 |
| 12 | 8206299070200 |
| 13 | 191673262380600 |
| 14 | 6154270418696400 |
| 15 | 206515993375692000 |
| 16 | 6574758436640394000 |
| 17 | 269828090984990538000 |
| 18 | 9531096165082736244000 |
| 19 | 411037724983993923816000 |
[1,1,2,36,234,7290,54540,1408680,23119740, 341788860,11790437400,231972879600,8206299070200, 191673262380600,6154270418696400, 206515993375692000,6574758436640394000, 269828090984990538000,9531096165082736244000, 411037724983993923816000] |