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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 20 |
| 3 | 284 |
| 4 | 4712 |
| 5 | 85392 |
| 6 | 1638112 |
| 7 | 32699472 |
| 8 | 672188768 |
| 9 | 14133399744 |
| 10 | 302535052160 |
| 11 | 6570819330688 |
| 12 | 144442463464704 |
| 13 | 3207564324825600 |
| 14 | 71848240540852224 |
| 15 | 1621452789508328704 |
| 16 | 36831997860270007808 |
| 17 | 841470878382566444032 |
[1,2,20,284,4712,85392,1638112,32699472,672188768, 14133399744,302535052160,6570819330688, 144442463464704,3207564324825600, 71848240540852224,1621452789508328704, 36831997860270007808,841470878382566444032] |