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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 20 |
| 2 | 330 |
| 3 | 5020 |
| 4 | 72955 |
| 5 | 1029420 |
| 6 | 14227600 |
| 7 | 193635980 |
| 8 | 2604170265 |
| 9 | 34691889640 |
| 10 | 458581416780 |
| 11 | 6022789170900 |
| 12 | 78668860592525 |
| 13 | 1022751344748320 |
| 14 | 13242477343206240 |
| 15 | 170851800208298220 |
| 16 | 2197361112206094725 |
| 17 | 28181571347810442300 |
| 18 | 360526760664147197350 |
| 19 | 4601781890365945572280 |
[1,20,330,5020,72955,1029420,14227600,193635980, 2604170265,34691889640,458581416780,6022789170900, 78668860592525,1022751344748320,13242477343206240, 170851800208298220,2197361112206094725, 28181571347810442300,360526760664147197350, 4601781890365945572280] |