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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 7 |
| 3 | 86 |
| 4 | 1524 |
| 5 | 35370 |
| 6 | 1015590 |
| 7 | 34757400 |
| 8 | 1381147440 |
| 9 | 62498177880 |
| 10 | 3172764322680 |
| 11 | 178566159846480 |
| 12 | 11034757650750960 |
| 13 | 742773843654742080 |
| 14 | 54094804600076176320 |
| 15 | 4238009228531321452800 |
| 16 | 355400361455423327193600 |
| 17 | 31764402860426288679456000 |
| 18 | 3014207878695233997923193600 |
[1,1,7,86,1524,35370,1015590,34757400,1381147440, 62498177880,3172764322680,178566159846480, 11034757650750960,742773843654742080, 54094804600076176320,4238009228531321452800, 355400361455423327193600, 31764402860426288679456000, 3014207878695233997923193600] |