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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 18 |
| 3 | 90 |
| 4 | 270 |
| 5 | 1134 |
| 6 | 5670 |
| 7 | 2430 |
| 8 | 7290 |
| 9 | 133650 |
| 10 | 112266 |
| 11 | 1990170 |
| 12 | 9950850 |
| 13 | 2296350 |
| 14 | 984150 |
| 15 | 117113850 |
| 16 | 351341550 |
| 17 | 33657930 |
| 18 | 21597171750 |
| 19 | 3410079750 |
| 20 | 572893398 |
| 21 | 33613643250 |
| 22 | 834229509750 |
| 23 | 108812544750 |
| 24 | 544062723750 |
| 25 | 18280507518 |
| 26 | 105464466450 |
| 27 | 18690647109750 |
[1,3,18,90,270,1134,5670,2430,7290,133650,112266, 1990170,9950850,2296350,984150,117113850, 351341550,33657930,21597171750,3410079750, 572893398,33613643250,834229509750,108812544750, 544062723750,18280507518,105464466450, 18690647109750] |