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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 60 |
| 5 | 504 |
| 6 | 4946 |
| 7 | 54430 |
| 8 | 655362 |
| 9 | 8496454 |
| 10 | 117311198 |
| 11 | 1711459903 |
| 12 | 26228829200 |
| 13 | 420370445830 |
| 14 | 7021029571856 |
| 15 | 121859518887327 |
| 16 | 2192820745899978 |
| 17 | 40831103986939664 |
| 18 | 785429260324068156 |
| 19 | 15585831041632684997 |
| 20 | 318649154587152781210 |
[1,1,2,9,60,504,4946,54430,655362,8496454, 117311198,1711459903,26228829200,420370445830, 7021029571856,121859518887327,2192820745899978, 40831103986939664,785429260324068156, 15585831041632684997,318649154587152781210] |