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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 30 |
| 4 | 330 |
| 5 | 4290 |
| 6 | 72930 |
| 7 | 2114970 |
| 8 | 65564070 |
| 9 | 2688126870 |
| 10 | 115589455410 |
| 11 | 5432704404270 |
| 12 | 320529559851930 |
| 13 | 21475480510079310 |
| 14 | 1567710077235789630 |
| 15 | 123849096101627380770 |
| 16 | 10279474976435072603910 |
| 17 | 1038226972619942332994910 |
| 18 | 113166740015573714296445190 |
| 19 | 12787841621759829715498306470 |
[1,2,6,30,330,4290,72930,2114970,65564070, 2688126870,115589455410,5432704404270, 320529559851930,21475480510079310, 1567710077235789630,123849096101627380770, 10279474976435072603910,1038226972619942332994910, 113166740015573714296445190, 12787841621759829715498306470] |