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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 15 |
| 3 | 100 |
| 4 | 819 |
| 5 | 7890 |
| 6 | 86995 |
| 7 | 1077150 |
| 8 | 14767575 |
| 9 | 221751010 |
| 10 | 3615510375 |
| 11 | 63552101550 |
| 12 | 1197196399675 |
| 13 | 24048396026850 |
| 14 | 512872089970875 |
| 15 | 11569027674987550 |
| 16 | 275113466366738175 |
| 17 | 6876716833964911650 |
| 18 | 180206071050892236175 |
| 19 | 4939209747546747991950 |
| 20 | 141294422480371952482275 |
[1,3,15,100,819,7890,86995,1077150,14767575, 221751010,3615510375,63552101550,1197196399675, 24048396026850,512872089970875,11569027674987550, 275113466366738175,6876716833964911650, 180206071050892236175,4939209747546747991950, 141294422480371952482275] |