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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 9 |
| 4 | 60 |
| 5 | 495 |
| 6 | 4986 |
| 7 | 58401 |
| 8 | 780984 |
| 9 | 11749779 |
| 10 | 196446870 |
| 11 | 3612882933 |
| 12 | 72484364052 |
| 13 | 1575418827879 |
| 14 | 36875093680530 |
| 15 | 924769734574185 |
| 16 | 24737895033896304 |
| 17 | 703105981990977915 |
| 18 | 21159355356941587470 |
| 19 | 672148402091190649629 |
| 20 | 22475238194908656800460 |
[1,0,2,9,60,495,4986,58401,780984,11749779, 196446870,3612882933,72484364052,1575418827879, 36875093680530,924769734574185,24737895033896304, 703105981990977915,21159355356941587470, 672148402091190649629,22475238194908656800460] |