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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 21 |
| 4 | 147 |
| 5 | 1250 |
| 6 | 12633 |
| 7 | 147497 |
| 8 | 1947676 |
| 9 | 28699373 |
| 10 | 466994003 |
| 11 | 8309274754 |
| 12 | 160368858609 |
| 13 | 3336869582657 |
| 14 | 74468098634660 |
| 15 | 1773827462044421 |
| 16 | 44905503103938915 |
| 17 | 1203843692164105458 |
| 18 | 34070243272290551113 |
| 19 | 1015056385225183643721 |
[1,1,4,21,147,1250,12633,147497,1947676,28699373, 466994003,8309274754,160368858609,3336869582657, 74468098634660,1773827462044421,44905503103938915, 1203843692164105458,34070243272290551113, 1015056385225183643721] |