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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 25 |
| 5 | 200 |
| 6 | 1890 |
| 7 | 20248 |
| 8 | 240069 |
| 9 | 3102000 |
| 10 | 43226590 |
| 11 | 644778520 |
| 12 | 10237504810 |
| 13 | 172274940656 |
| 14 | 3061868388100 |
| 15 | 57310884482160 |
| 16 | 1126953452418765 |
| 17 | 23230411494361920 |
| 18 | 501015558669312390 |
| 19 | 11285603304699928600 |
| 20 | 265077311648541268030 |
| 21 | 6482435029801210815280 |
[1,1,4,25,200,1890,20248,240069,3102000,43226590, 644778520,10237504810,172274940656,3061868388100, 57310884482160,1126953452418765,23230411494361920, 501015558669312390,11285603304699928600, 265077311648541268030,6482435029801210815280] |