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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 20 |
| 2 | 380 |
| 3 | 7220 |
| 4 | 137180 |
| 5 | 2606420 |
| 6 | 49521980 |
| 7 | 940917620 |
| 8 | 17877434780 |
| 9 | 339671260820 |
| 10 | 6453753955580 |
| 11 | 122621325156020 |
| 12 | 2329805177964380 |
| 13 | 44266298381323220 |
| 14 | 841059669245141180 |
| 15 | 15980133715657682420 |
[1,20,380,7220,137180,2606420,49521980,940917620, 17877434780,339671260820,6453753955580, 122621325156020,2329805177964380, 44266298381323220,841059669245141180, 15980133715657682420] |