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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 12 |
| 4 | 108 |
| 5 | 1360 |
| 6 | 21780 |
| 7 | 424998 |
| 8 | 9774912 |
| 9 | 259012080 |
| 10 | 7769656800 |
| 11 | 260283596760 |
| 12 | 9631680917760 |
| 13 | 390185658289128 |
| 14 | 17175153440774784 |
| 15 | 816267894739416000 |
| 16 | 41658264473400852480 |
| 17 | 2272233977181361580160 |
| 18 | 131913883517800157429760 |
| 19 | 8121310193676734923381056 |
[1,1,2,12,108,1360,21780,424998,9774912,259012080, 7769656800,260283596760,9631680917760, 390185658289128,17175153440774784, 816267894739416000,41658264473400852480, 2272233977181361580160,131913883517800157429760, 8121310193676734923381056] |