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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 721 |
| 7 | 5075 |
| 8 | 41146 |
| 9 | 379764 |
| 10 | 3955413 |
| 11 | 46147101 |
| 12 | 598757159 |
| 13 | 8574963397 |
| 14 | 134469746411 |
| 15 | 2290379988897 |
| 16 | 42043096791696 |
| 17 | 825840722368662 |
| 18 | 17251010028434182 |
| 19 | 381214917773329640 |
| 20 | 8873155199416851343 |
| 21 | 216770612918353773279 |
| 22 | 5542237907509303118118 |
[1,1,2,6,24,120,721,5075,41146,379764,3955413, 46147101,598757159,8574963397,134469746411, 2290379988897,42043096791696,825840722368662, 17251010028434182,381214917773329640, 8873155199416851343,216770612918353773279, 5542237907509303118118] |