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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 6 |
| 3 | 66 |
| 4 | 210 |
| 5 | 3570 |
| 6 | 207690 |
| 7 | 930930 |
| 8 | 56812470 |
| 9 | 1803571770 |
| 10 | 32395433070 |
| 11 | 265257422430 |
| 12 | 91348974206490 |
| 13 | 24630635909489610 |
| 14 | 438603767516904990 |
| 15 | 14193386885746698630 |
| 16 | 2378522762792139793830 |
| 17 | 351206814022419685159830 |
| 18 | 28791787439593010836313310 |
[1,3,6,66,210,3570,207690,930930,56812470, 1803571770,32395433070,265257422430, 91348974206490,24630635909489610, 438603767516904990,14193386885746698630, 2378522762792139793830,351206814022419685159830, 28791787439593010836313310] |