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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 31 |
| 4 | 289 |
| 5 | 3495 |
| 6 | 51268 |
| 7 | 891152 |
| 8 | 17926913 |
| 9 | 409907600 |
| 10 | 10499834497 |
| 11 | 297793199060 |
| 12 | 9262502810645 |
| 13 | 313457634240463 |
| 14 | 11464902463397642 |
| 15 | 450646709610954343 |
| 16 | 18943070964019019671 |
| 17 | 847932498252050293971 |
| 18 | 40266255926484893366914 |
| 19 | 2021845081107882645459639 |
[1,1,4,31,289,3495,51268,891152,17926913, 409907600,10499834497,297793199060,9262502810645, 313457634240463,11464902463397642, 450646709610954343,18943070964019019671, 847932498252050293971,40266255926484893366914, 2021845081107882645459639] |