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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 5 |
| 3 | 42 |
| 4 | 498 |
| 5 | 7644 |
| 6 | 144156 |
| 7 | 3225648 |
| 8 | 83536008 |
| 9 | 2457701928 |
| 10 | 80970232104 |
| 11 | 2953056534768 |
| 12 | 118112744060208 |
| 13 | 5140622709134496 |
| 14 | 241863782829704928 |
| 15 | 12232551538417012992 |
| 16 | 661818290353375962240 |
| 17 | 38140594162828447248000 |
| 18 | 2332567001993176540206720 |
| 19 | 150880256846462633823648000 |
[1,1,5,42,498,7644,144156,3225648,83536008, 2457701928,80970232104,2953056534768, 118112744060208,5140622709134496, 241863782829704928,12232551538417012992, 661818290353375962240,38140594162828447248000, 2332567001993176540206720, 150880256846462633823648000] |